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 $196.52   12.613%   $221.3071   $221.31   $221.30   $221.30  
  Purchase #2 $151.72   5.570%   $160.1708   $160.17   $160.15   $160.20  
  Purchase #3 $141.37   11.610%   $157.7831   $157.78   $157.80   $157.80  
  Purchase #4 $228.89   9.696%   $251.0832   $251.08   $251.10   $251.10  
  Purchase #5 $60.33   3.408%   $62.386   $62.39   $62.40   $62.40  
  Purchase #6 $205.29   3.323%   $212.1118   $212.11   $212.10   $212.10  
  Purchase #7 $119.90   10.338%   $132.2953   $132.30   $132.30   $132.30  
  7 purchase totals = $1,104.02       $1,197.1373   $1,197.14   $1,197.15   $1,197.20