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 $202.75   5.338%   $213.5728   $213.57   $213.55   $213.60  
  Purchase #2 $91.56   4.760%   $95.9183   $95.92   $95.90   $95.90  
  Purchase #3 $83.83   11.154%   $93.1804   $93.18   $93.20   $93.20  
  Purchase #4 $230.66   5.740%   $243.8999   $243.90   $243.90   $243.90  
  Purchase #5 $14.87   13.761%   $16.9163   $16.92   $16.90   $16.90  
  Purchase #6 $77.42   3.252%   $79.9377   $79.94   $79.95   $79.90  
  Purchase #7 $245.78   5.375%   $258.9907   $258.99   $259.00   $259.00  
  7 purchase totals = $946.87       $1,002.4161   $1,002.42   $1,002.40   $1,002.40