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 $85.87   7.322%   $92.1574   $92.16   $92.15   $92.20  
  Purchase #2 $238.57   4.737%   $249.8711   $249.87   $249.85   $249.90  
  Purchase #3 $43.61   11.247%   $48.5148   $48.51   $48.50   $48.50  
  Purchase #4 $191.65   5.616%   $202.4131   $202.41   $202.40   $202.40  
  Purchase #5 $221.80   12.278%   $249.0326   $249.03   $249.05   $249.00  
  Purchase #6 $102.72   8.702%   $111.6587   $111.66   $111.65   $111.70  
  Purchase #7 $40.81   3.830%   $42.373   $42.37   $42.35   $42.40  
  7 purchase totals = $925.03       $996.0207   $996.01   $995.95   $996.10