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 $250.73   9.484%   $274.5092   $274.51   $274.50   $274.50  
  Purchase #2 $52.79   11.863%   $59.0525   $59.05   $59.05   $59.10  
  Purchase #3 $112.55   3.717%   $116.7335   $116.73   $116.75   $116.70  
  Purchase #4 $82.55   5.374%   $86.9862   $86.99   $87.00   $87.00  
  Purchase #5 $207.35   3.122%   $213.8235   $213.82   $213.80   $213.80  
  Purchase #6 $23.99   9.131%   $26.1805   $26.18   $26.20   $26.20  
  Purchase #7 $150.90   3.199%   $155.7273   $155.73   $155.75   $155.70  
  7 purchase totals = $880.86       $933.0127   $933.01   $933.05   $933.00