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 $192.92   4.873%   $202.321   $202.32   $202.30   $202.30  
  Purchase #2 $149.46   4.331%   $155.9331   $155.93   $155.95   $155.90  
  Purchase #3 $150.62   5.391%   $158.7399   $158.74   $158.75   $158.70  
  Purchase #4 $202.72   5.253%   $213.3689   $213.37   $213.35   $213.40  
  Purchase #5 $76.35   8.546%   $82.8749   $82.87   $82.85   $82.90  
  Purchase #6 $105.99   9.630%   $116.1968   $116.20   $116.20   $116.20  
  Purchase #7 $245.60   9.131%   $268.0257   $268.03   $268.05   $268.00  
  7 purchase totals = $1,123.66       $1,197.4603   $1,197.46   $1,197.45   $1,197.40