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 $90.43   6.187%   $96.0249   $96.02   $96.00   $96.00  
  Purchase #2 $149.90   4.179%   $156.1643   $156.16   $156.15   $156.20  
  Purchase #3 $219.42   6.555%   $233.803   $233.80   $233.80   $233.80  
  Purchase #4 $197.55   9.743%   $216.7973   $216.80   $216.80   $216.80  
  Purchase #5 $51.30   9.604%   $56.2269   $56.23   $56.25   $56.20  
  Purchase #6 $57.25   10.152%   $63.062   $63.06   $63.05   $63.10  
  Purchase #7 $27.64   6.598%   $29.4637   $29.46   $29.45   $29.50  
  7 purchase totals = $793.49       $851.5421   $851.53   $851.50   $851.60