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 $52.29   12.811%   $58.9889   $58.99   $59.00   $59.00  
  Purchase #2 $121.69   3.626%   $126.1025   $126.10   $126.10   $126.10  
  Purchase #3 $129.46   12.374%   $145.4794   $145.48   $145.50   $145.50  
  Purchase #4 $158.29   5.548%   $167.0719   $167.07   $167.05   $167.10  
  Purchase #5 $122.33   4.847%   $128.2593   $128.26   $128.25   $128.30  
  Purchase #6 $141.53   7.366%   $151.9551   $151.96   $151.95   $152.00  
  Purchase #7 $172.79   12.321%   $194.0795   $194.08   $194.10   $194.10  
  7 purchase totals = $898.38       $971.9366   $971.94   $971.95   $972.10