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 $228.51   8.490%   $247.9105   $247.91   $247.90   $247.90  
  Purchase #2 $88.88   7.516%   $95.5602   $95.56   $95.55   $95.60  
  Purchase #3 $5.73   13.568%   $6.5074   $6.51   $6.50   $6.50  
  Purchase #4 $102.37   12.285%   $114.9462   $114.95   $114.95   $114.90  
  Purchase #5 $239.53   11.779%   $267.7442   $267.74   $267.75   $267.70  
  Purchase #6 $180.83   13.183%   $204.6688   $204.67   $204.65   $204.70  
  Purchase #7 $33.46   7.584%   $35.9976   $36.00   $36.00   $36.00  
  7 purchase totals = $879.31       $973.3349   $973.34   $973.30   $973.30