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 $65.93   4.712%   $69.0366   $69.04   $69.05   $69.00  
  Purchase #2 $57.79   7.827%   $62.3132   $62.31   $62.30   $62.30  
  Purchase #3 $93.84   7.692%   $101.0582   $101.06   $101.05   $101.10  
  Purchase #4 $34.30   6.198%   $36.4259   $36.43   $36.45   $36.40  
  Purchase #5 $170.71   9.191%   $186.4   $186.40   $186.40   $186.40  
  Purchase #6 $215.29   7.783%   $232.046   $232.05   $232.05   $232.00  
  Purchase #7 $66.80   8.479%   $72.464   $72.46   $72.45   $72.50  
  7 purchase totals = $704.66       $759.7439   $759.75   $759.75   $759.70