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 $92.81   12.850%   $104.7361   $104.74   $104.75   $104.70  
  Purchase #2 $161.33   12.396%   $181.3285   $181.33   $181.35   $181.30  
  Purchase #3 $110.54   13.441%   $125.3977   $125.40   $125.40   $125.40  
  Purchase #4 $202.64   11.585%   $226.1158   $226.12   $226.10   $226.10  
  Purchase #5 $200.54   3.500%   $207.5589   $207.56   $207.55   $207.60  
  Purchase #6 $166.55   13.670%   $189.3174   $189.32   $189.30   $189.30  
  Purchase #7 $61.71   8.511%   $66.9621   $66.96   $66.95   $67.00  
  7 purchase totals = $996.12       $1,101.4165   $1,101.43   $1,101.40   $1,101.40