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 $32.97   11.435%   $36.7401   $36.74   $36.75   $36.70  
  Purchase #2 $60.93   9.117%   $66.485   $66.49   $66.50   $66.50  
  Purchase #3 $217.87   11.531%   $242.9926   $242.99   $243.00   $243.00  
  Purchase #4 $77.49   8.801%   $84.3099   $84.31   $84.30   $84.30  
  Purchase #5 $81.52   4.661%   $85.3196   $85.32   $85.30   $85.30  
  Purchase #6 $166.74   5.648%   $176.1575   $176.16   $176.15   $176.20  
  Purchase #7 $43.94   3.104%   $45.3039   $45.30   $45.30   $45.30  
  7 purchase totals = $681.46       $737.3086   $737.31   $737.30   $737.30