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 $203.59   5.208%   $214.193   $214.19   $214.20   $214.20  
  Purchase #2 $109.46   6.554%   $116.634   $116.63   $116.65   $116.60  
  Purchase #3 $137.79   12.641%   $155.208   $155.21   $155.20   $155.20  
  Purchase #4 $31.97   7.638%   $34.4119   $34.41   $34.40   $34.40  
  Purchase #5 $202.88   3.773%   $210.5347   $210.53   $210.55   $210.50  
  Purchase #6 $93.45   11.111%   $103.8332   $103.83   $103.85   $103.80  
  Purchase #7 $90.45   13.819%   $102.9493   $102.95   $102.95   $102.90  
  7 purchase totals = $869.59       $937.7641   $937.75   $937.80   $937.60