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 $129.73   3.654%   $134.4703   $134.47   $134.45   $134.50  
  Purchase #2 $156.78   12.392%   $176.2082   $176.21   $176.20   $176.20  
  Purchase #3 $122.46   3.291%   $126.4902   $126.49   $126.50   $126.50  
  Purchase #4 $59.56   11.281%   $66.279   $66.28   $66.30   $66.30  
  Purchase #5 $148.85   7.218%   $159.594   $159.59   $159.60   $159.60  
  Purchase #6 $211.41   4.528%   $220.9826   $220.98   $221.00   $221.00  
  Purchase #7 $233.59   3.275%   $241.2401   $241.24   $241.25   $241.20  
  7 purchase totals = $1,062.38       $1,125.2644   $1,125.26   $1,125.30   $1,125.30