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 $67.55   13.608%   $76.7422   $76.74   $76.75   $76.70  
  Purchase #2 $46.26   9.459%   $50.6357   $50.64   $50.65   $50.60  
  Purchase #3 $130.26   5.802%   $137.8177   $137.82   $137.80   $137.80  
  Purchase #4 $192.54   5.537%   $203.2009   $203.20   $203.20   $203.20  
  Purchase #5 $205.82   7.268%   $220.779   $220.78   $220.80   $220.80  
  Purchase #6 $25.59   13.810%   $29.124   $29.12   $29.10   $29.10  
  Purchase #7 $94.88   7.813%   $102.293   $102.29   $102.30   $102.30  
  7 purchase totals = $762.90       $820.5925   $820.59   $820.60   $820.50