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 $69.33   12.144%   $77.7494   $77.75   $77.75   $77.70  
  Purchase #2 $224.72   10.234%   $247.7178   $247.72   $247.70   $247.70  
  Purchase #3 $60.64   13.359%   $68.7409   $68.74   $68.75   $68.70  
  Purchase #4 $6.49   12.383%   $7.2937   $7.29   $7.30   $7.30  
  Purchase #5 $243.97   10.565%   $269.7454   $269.75   $269.75   $269.70  
  Purchase #6 $187.84   4.584%   $196.4506   $196.45   $196.45   $196.50  
  Purchase #7 $48.91   11.504%   $54.5366   $54.54   $54.55   $54.50  
  7 purchase totals = $841.90       $922.2344   $922.24   $922.25   $922.10