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 $230.63   7.432%   $247.7704   $247.77   $247.75   $247.80  
  Purchase #2 $79.29   11.829%   $88.6692   $88.67   $88.65   $88.70  
  Purchase #3 $209.88   7.669%   $225.9757   $225.98   $226.00   $226.00  
  Purchase #4 $232.36   4.617%   $243.0881   $243.09   $243.10   $243.10  
  Purchase #5 $176.53   11.544%   $196.9086   $196.91   $196.90   $196.90  
  Purchase #6 $199.89   8.283%   $216.4469   $216.45   $216.45   $216.40  
  Purchase #7 $94.38   12.393%   $106.0765   $106.08   $106.10   $106.10  
  7 purchase totals = $1,222.96       $1,324.9354   $1,324.95   $1,324.95   $1,325.00