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 $48.70   8.722%   $52.9476   $52.95   $52.95   $52.90  
  Purchase #2 $82.28   11.330%   $91.6023   $91.60   $91.60   $91.60  
  Purchase #3 $195.93   3.428%   $202.6465   $202.65   $202.65   $202.60  
  Purchase #4 $147.25   9.737%   $161.5877   $161.59   $161.60   $161.60  
  Purchase #5 $117.39   7.635%   $126.3527   $126.35   $126.35   $126.40  
  Purchase #6 $191.61   3.113%   $197.5748   $197.57   $197.55   $197.60  
  Purchase #7 $102.96   12.491%   $115.8207   $115.82   $115.80   $115.80  
  7 purchase totals = $886.12       $948.5323   $948.53   $948.50   $948.50