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 $230.73   13.104%   $260.9649   $260.96   $260.95   $261.00  
  Purchase #2 $192.38   9.435%   $210.5311   $210.53   $210.55   $210.50  
  Purchase #3 $221.56   10.824%   $245.5417   $245.54   $245.55   $245.50  
  Purchase #4 $5.59   3.631%   $5.793   $5.79   $5.80   $5.80  
  Purchase #5 $168.83   10.194%   $186.0405   $186.04   $186.05   $186.00  
  Purchase #6 $154.93   12.447%   $174.2141   $174.21   $174.20   $174.20  
  Purchase #7 $94.62   8.764%   $102.9125   $102.91   $102.90   $102.90  
  7 purchase totals = $1,068.64       $1,185.9978   $1,185.98   $1,186.00   $1,185.90