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 $184.96   9.628%   $202.7679   $202.77   $202.75   $202.80  
  Purchase #2 $72.39   9.507%   $79.2721   $79.27   $79.25   $79.30  
  Purchase #3 $56.48   6.218%   $59.9919   $59.99   $60.00   $60.00  
  Purchase #4 $148.39   4.363%   $154.8643   $154.86   $154.85   $154.90  
  Purchase #5 $85.59   11.260%   $95.2274   $95.23   $95.25   $95.20  
  Purchase #6 $118.75   4.727%   $124.3633   $124.36   $124.35   $124.40  
  Purchase #7 $30.72   10.636%   $33.9874   $33.99   $34.00   $34.00  
  7 purchase totals = $697.28       $750.4743   $750.47   $750.45   $750.60