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 $212.42   6.817%   $226.9007   $226.90   $226.90   $226.90  
  Purchase #2 $173.81   4.218%   $181.1413   $181.14   $181.15   $181.10  
  Purchase #3 $85.34   3.414%   $88.2535   $88.25   $88.25   $88.30  
  Purchase #4 $170.46   12.455%   $191.6908   $191.69   $191.70   $191.70  
  Purchase #5 $221.79   9.821%   $243.572   $243.57   $243.55   $243.60  
  Purchase #6 $7.62   4.870%   $7.9911   $7.99   $8.00   $8.00  
  Purchase #7 $59.26   8.237%   $64.1412   $64.14   $64.15   $64.10  
  7 purchase totals = $930.70       $1,003.6906   $1,003.68   $1,003.70   $1,003.70