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 $53.97   6.198%   $57.3151   $57.32   $57.30   $57.30  
  Purchase #2 $144.38   8.408%   $156.5195   $156.52   $156.50   $156.50  
  Purchase #3 $72.28   11.359%   $80.4903   $80.49   $80.50   $80.50  
  Purchase #4 $13.38   3.484%   $13.8462   $13.85   $13.85   $13.80  
  Purchase #5 $162.43   13.123%   $183.7457   $183.75   $183.75   $183.70  
  Purchase #6 $63.67   7.363%   $68.358   $68.36   $68.35   $68.40  
  Purchase #7 $196.61   3.255%   $203.0097   $203.01   $203.00   $203.00  
  7 purchase totals = $706.72       $763.2845   $763.30   $763.25   $763.20