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 $148.55   3.193%   $153.2932   $153.29   $153.30   $153.30  
  Purchase #2 $213.63   7.401%   $229.4408   $229.44   $229.45   $229.40  
  Purchase #3 $207.44   4.479%   $216.7312   $216.73   $216.75   $216.70  
  Purchase #4 $188.45   12.807%   $212.5848   $212.58   $212.60   $212.60  
  Purchase #5 $51.64   9.213%   $56.3976   $56.40   $56.40   $56.40  
  Purchase #6 $245.32   12.219%   $275.2957   $275.30   $275.30   $275.30  
  Purchase #7 $109.52   4.377%   $114.3137   $114.31   $114.30   $114.30  
  7 purchase totals = $1,164.55       $1,258.0570   $1,258.05   $1,258.10   $1,258.00