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 $48.97   11.372%   $54.5389   $54.54   $54.55   $54.50  
  Purchase #2 $244.73   8.352%   $265.1698   $265.17   $265.15   $265.20  
  Purchase #3 $96.36   6.186%   $102.3208   $102.32   $102.30   $102.30  
  Purchase #4 $78.25   5.218%   $82.3331   $82.33   $82.35   $82.30  
  Purchase #5 $177.25   11.258%   $197.2048   $197.20   $197.20   $197.20  
  Purchase #6 $111.57   5.869%   $118.118   $118.12   $118.10   $118.10  
  Purchase #7 $183.87   7.385%   $197.4488   $197.45   $197.45   $197.40  
  7 purchase totals = $941.00       $1,017.1342   $1,017.13   $1,017.10   $1,017.00