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 $52.95   11.842%   $59.2203   $59.22   $59.20   $59.20  
  Purchase #2 $215.29   5.270%   $226.6358   $226.64   $226.65   $226.60  
  Purchase #3 $87.40   7.654%   $94.0896   $94.09   $94.10   $94.10  
  Purchase #4 $117.34   7.640%   $126.3048   $126.30   $126.30   $126.30  
  Purchase #5 $222.61   12.214%   $249.7996   $249.80   $249.80   $249.80  
  Purchase #6 $12.90   3.529%   $13.3552   $13.36   $13.35   $13.40  
  Purchase #7 $157.77   11.226%   $175.4813   $175.48   $175.50   $175.50  
  7 purchase totals = $866.26       $944.8866   $944.89   $944.90   $944.90