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 $56.72   10.651%   $62.7612   $62.76   $62.75   $62.80  
  Purchase #2 $229.67   6.247%   $244.0175   $244.02   $244.00   $244.00  
  Purchase #3 $129.97   6.150%   $137.9632   $137.96   $137.95   $138.00  
  Purchase #4 $32.35   4.457%   $33.7918   $33.79   $33.80   $33.80  
  Purchase #5 $61.40   11.633%   $68.5427   $68.54   $68.55   $68.50  
  Purchase #6 $119.32   7.277%   $128.0029   $128.00   $128.00   $128.00  
  Purchase #7 $105.67   9.402%   $115.6051   $115.61   $115.60   $115.60  
  7 purchase totals = $735.10       $790.6844   $790.68   $790.65   $790.70