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 $28.67   12.133%   $32.1485   $32.15   $32.15   $32.10  
  Purchase #2 $152.34   6.145%   $161.7013   $161.70   $161.70   $161.70  
  Purchase #3 $113.50   4.407%   $118.5019   $118.50   $118.50   $118.50  
  Purchase #4 $188.40   3.343%   $194.6982   $194.70   $194.70   $194.70  
  Purchase #5 $21.96   9.220%   $23.9847   $23.98   $24.00   $24.00  
  Purchase #6 $97.37   3.755%   $101.0262   $101.03   $101.05   $101.00  
  Purchase #7 $244.35   7.784%   $263.3702   $263.37   $263.35   $263.40  
  7 purchase totals = $846.59       $895.4310   $895.43   $895.45   $895.40