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 $45.42   13.399%   $51.5058   $51.51   $51.50   $51.50  
  Purchase #2 $25.39   7.316%   $27.2475   $27.25   $27.25   $27.20  
  Purchase #3 $224.64   7.613%   $241.7418   $241.74   $241.75   $241.70  
  Purchase #4 $115.67   7.293%   $124.1058   $124.11   $124.10   $124.10  
  Purchase #5 $103.92   8.753%   $113.0161   $113.02   $113.00   $113.00  
  Purchase #6 $211.57   4.511%   $221.1139   $221.11   $221.10   $221.10  
  Purchase #7 $207.34   13.531%   $235.3952   $235.40   $235.40   $235.40  
  7 purchase totals = $933.95       $1,014.1261   $1,014.14   $1,014.10   $1,014.00