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 $44.62   11.210%   $49.6219   $49.62   $49.60   $49.60  
  Purchase #2 $221.74   3.785%   $230.1329   $230.13   $230.15   $230.10  
  Purchase #3 $143.70   13.155%   $162.6037   $162.60   $162.60   $162.60  
  Purchase #4 $17.77   5.547%   $18.7557   $18.76   $18.75   $18.80  
  Purchase #5 $180.60   13.449%   $204.8889   $204.89   $204.90   $204.90  
  Purchase #6 $220.77   12.170%   $247.6377   $247.64   $247.65   $247.60  
  Purchase #7 $138.31   11.844%   $154.6914   $154.69   $154.70   $154.70  
  7 purchase totals = $967.51       $1,068.3322   $1,068.33   $1,068.35   $1,068.30