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 $113.72   4.358%   $118.6759   $118.68   $118.70   $118.70  
  Purchase #2 $210.92   6.124%   $223.8367   $223.84   $223.85   $223.80  
  Purchase #3 $209.26   4.614%   $218.9153   $218.92   $218.90   $218.90  
  Purchase #4 $81.81   7.555%   $87.9907   $87.99   $88.00   $88.00  
  Purchase #5 $180.81   7.703%   $194.7378   $194.74   $194.75   $194.70  
  Purchase #6 $209.29   4.112%   $217.896   $217.90   $217.90   $217.90  
  Purchase #7 $177.78   13.327%   $201.4727   $201.47   $201.45   $201.50  
  7 purchase totals = $1,183.59       $1,263.5251   $1,263.54   $1,263.55   $1,263.50