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 $110.29   8.344%   $119.4926   $119.49   $119.50   $119.50  
  Purchase #2 $61.92   5.371%   $65.2457   $65.25   $65.25   $65.20  
  Purchase #3 $230.71   5.776%   $244.0358   $244.04   $244.05   $244.00  
  Purchase #4 $220.59   12.134%   $247.3564   $247.36   $247.35   $247.40  
  Purchase #5 $247.77   9.732%   $271.883   $271.88   $271.90   $271.90  
  Purchase #6 $160.32   6.256%   $170.3496   $170.35   $170.35   $170.30  
  Purchase #7 $50.73   5.159%   $53.3472   $53.35   $53.35   $53.30  
  7 purchase totals = $1,082.33       $1,171.7103   $1,171.72   $1,171.75   $1,171.60