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 $188.25   4.826%   $197.3349   $197.33   $197.35   $197.30  
  Purchase #2 $7.89   4.760%   $8.2656   $8.27   $8.25   $8.30  
  Purchase #3 $122.45   13.832%   $139.3873   $139.39   $139.40   $139.40  
  Purchase #4 $246.45   11.695%   $275.2723   $275.27   $275.25   $275.30  
  Purchase #5 $53.87   12.125%   $60.4017   $60.40   $60.40   $60.40  
  Purchase #6 $104.49   4.238%   $108.9183   $108.92   $108.90   $108.90  
  Purchase #7 $217.80   13.186%   $246.5191   $246.52   $246.50   $246.50  
  7 purchase totals = $941.20       $1,036.0992   $1,036.10   $1,036.05   $1,036.10