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 $54.98   8.637%   $59.7286   $59.73   $59.75   $59.70  
  Purchase #2 $107.88   9.285%   $117.8967   $117.90   $117.90   $117.90  
  Purchase #3 $240.47   3.189%   $248.1386   $248.14   $248.15   $248.10  
  Purchase #4 $205.63   12.780%   $231.9095   $231.91   $231.90   $231.90  
  Purchase #5 $176.51   10.841%   $195.6454   $195.65   $195.65   $195.60  
  Purchase #6 $168.53   12.525%   $189.6384   $189.64   $189.65   $189.60  
  Purchase #7 $19.79   3.853%   $20.5525   $20.55   $20.55   $20.60  
  7 purchase totals = $973.79       $1,063.5097   $1,063.52   $1,063.55   $1,063.40