Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $174.80   4.467%   $182.6083   $182.61   $182.60   $182.60  
  Purchase #2 $241.61   10.189%   $266.2276   $266.23   $266.25   $266.20  
  Purchase #3 $240.96   8.157%   $260.6151   $260.62   $260.60   $260.60  
  Purchase #4 $191.42   5.312%   $201.5882   $201.59   $201.60   $201.60  
  Purchase #5 $174.64   12.790%   $196.9765   $196.98   $197.00   $197.00  
  Purchase #6 $121.46   10.408%   $134.1016   $134.10   $134.10   $134.10  
  Purchase #7 $137.86   8.842%   $150.0496   $150.05   $150.05   $150.00  
  7 purchase totals = $1,282.75       $1,392.1669   $1,392.18   $1,392.20   $1,392.10