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 $39.71   11.491%   $44.2731   $44.27   $44.25   $44.30  
  Purchase #2 $217.86   11.732%   $243.4193   $243.42   $243.40   $243.40  
  Purchase #3 $241.30   5.280%   $254.0406   $254.04   $254.05   $254.00  
  Purchase #4 $219.40   12.231%   $246.2348   $246.23   $246.25   $246.20  
  Purchase #5 $138.76   11.709%   $155.0074   $155.01   $155.00   $155.00  
  Purchase #6 $65.59   4.625%   $68.6235   $68.62   $68.60   $68.60  
  Purchase #7 $44.72   3.368%   $46.2262   $46.23   $46.25   $46.20  
  7 purchase totals = $967.34       $1,057.8249   $1,057.82   $1,057.80   $1,057.70