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 $203.90   4.644%   $213.3691   $213.37   $213.35   $213.40  
  Purchase #2 $115.56   4.659%   $120.9439   $120.94   $120.95   $120.90  
  Purchase #3 $88.35   13.865%   $100.5997   $100.60   $100.60   $100.60  
  Purchase #4 $52.79   11.355%   $58.7843   $58.78   $58.80   $58.80  
  Purchase #5 $67.49   5.485%   $71.1918   $71.19   $71.20   $71.20  
  Purchase #6 $7.43   3.835%   $7.7149   $7.71   $7.70   $7.70  
  Purchase #7 $9.56   3.842%   $9.9273   $9.93   $9.95   $9.90  
  7 purchase totals = $545.08       $582.5310   $582.52   $582.55   $582.50