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 $100.72   9.579%   $110.368   $110.37   $110.35   $110.40  
  Purchase #2 $157.37   9.795%   $172.7844   $172.78   $172.80   $172.80  
  Purchase #3 $13.35   3.791%   $13.8561   $13.86   $13.85   $13.90  
  Purchase #4 $105.58   12.788%   $119.0816   $119.08   $119.10   $119.10  
  Purchase #5 $196.73   6.427%   $209.3738   $209.37   $209.35   $209.40  
  Purchase #6 $134.95   13.538%   $153.2195   $153.22   $153.20   $153.20  
  Purchase #7 $144.80   9.745%   $158.9108   $158.91   $158.90   $158.90  
  7 purchase totals = $853.50       $937.5942   $937.59   $937.55   $937.70