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 $78.96   6.786%   $84.3182   $84.32   $84.30   $84.30  
  Purchase #2 $196.42   9.120%   $214.3335   $214.33   $214.35   $214.30  
  Purchase #3 $69.40   10.754%   $76.8633   $76.86   $76.85   $76.90  
  Purchase #4 $210.75   11.667%   $235.3382   $235.34   $235.35   $235.30  
  Purchase #5 $184.98   5.178%   $194.5583   $194.56   $194.55   $194.60  
  Purchase #6 $190.63   11.382%   $212.3275   $212.33   $212.35   $212.30  
  Purchase #7 $222.92   13.300%   $252.5684   $252.57   $252.55   $252.60  
  7 purchase totals = $1,154.06       $1,270.3074   $1,270.31   $1,270.30   $1,270.30