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 $170.95   7.756%   $184.2089   $184.21   $184.20   $184.20  
  Purchase #2 $91.53   4.283%   $95.4502   $95.45   $95.45   $95.50  
  Purchase #3 $46.49   9.238%   $50.7847   $50.78   $50.80   $50.80  
  Purchase #4 $152.35   7.305%   $163.4792   $163.48   $163.50   $163.50  
  Purchase #5 $207.81   11.735%   $232.1965   $232.20   $232.20   $232.20  
  Purchase #6 $105.67   6.229%   $112.2522   $112.25   $112.25   $112.30  
  Purchase #7 $234.55   4.391%   $244.8491   $244.85   $244.85   $244.80  
  7 purchase totals = $1,009.35       $1,083.2208   $1,083.22   $1,083.25   $1,083.30