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 $241.46   10.304%   $266.34   $266.34   $266.35   $266.30  
  Purchase #2 $126.35   5.231%   $132.9594   $132.96   $132.95   $133.00  
  Purchase #3 $228.71   8.224%   $247.5191   $247.52   $247.50   $247.50  
  Purchase #4 $177.58   6.707%   $189.4903   $189.49   $189.50   $189.50  
  Purchase #5 $76.78   12.557%   $86.4213   $86.42   $86.40   $86.40  
  Purchase #6 $60.69   8.850%   $66.0611   $66.06   $66.05   $66.10  
  Purchase #7 $174.42   13.548%   $198.0504   $198.05   $198.05   $198.10  
  7 purchase totals = $1,085.99       $1,186.8416   $1,186.84   $1,186.80   $1,186.90