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 $132.62   6.496%   $141.235   $141.24   $141.25   $141.20  
  Purchase #2 $120.50   5.360%   $126.9588   $126.96   $126.95   $127.00  
  Purchase #3 $148.63   3.230%   $153.4307   $153.43   $153.45   $153.40  
  Purchase #4 $189.53   3.112%   $195.4282   $195.43   $195.45   $195.40  
  Purchase #5 $99.97   12.337%   $112.3033   $112.30   $112.30   $112.30  
  Purchase #6 $71.51   13.801%   $81.3791   $81.38   $81.40   $81.40  
  Purchase #7 $190.71   5.400%   $201.0083   $201.01   $201.00   $201.00  
  7 purchase totals = $953.47       $1,011.7434   $1,011.75   $1,011.80   $1,011.70