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 $213.64   9.371%   $233.6602   $233.66   $233.65   $233.70  
  Purchase #2 $245.49   12.148%   $275.3121   $275.31   $275.30   $275.30  
  Purchase #3 $129.96   11.302%   $144.6481   $144.65   $144.65   $144.60  
  Purchase #4 $240.86   5.614%   $254.3819   $254.38   $254.40   $254.40  
  Purchase #5 $181.95   6.461%   $193.7058   $193.71   $193.70   $193.70  
  Purchase #6 $13.79   9.693%   $15.1267   $15.13   $15.15   $15.10  
  Purchase #7 $171.46   13.360%   $194.3671   $194.37   $194.35   $194.40  
  7 purchase totals = $1,197.15       $1,311.2019   $1,311.21   $1,311.20   $1,311.20