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 $202.47   8.492%   $219.6638   $219.66   $219.65   $219.70  
  Purchase #2 $35.92   4.193%   $37.4261   $37.43   $37.45   $37.40  
  Purchase #3 $117.66   7.872%   $126.9222   $126.92   $126.90   $126.90  
  Purchase #4 $52.98   12.477%   $59.5903   $59.59   $59.60   $59.60  
  Purchase #5 $140.44   5.256%   $147.8215   $147.82   $147.80   $147.80  
  Purchase #6 $138.79   9.546%   $152.0389   $152.04   $152.05   $152.00  
  Purchase #7 $162.60   7.847%   $175.3592   $175.36   $175.35   $175.40  
  7 purchase totals = $850.86       $918.8220   $918.82   $918.80   $918.80