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 $96.60   4.577%   $101.0214   $101.02   $101.00   $101.00  
  Purchase #2 $231.35   9.761%   $253.9321   $253.93   $253.95   $253.90  
  Purchase #3 $21.37   12.225%   $23.9825   $23.98   $24.00   $24.00  
  Purchase #4 $204.70   7.485%   $220.0218   $220.02   $220.00   $220.00  
  Purchase #5 $234.80   11.851%   $262.6261   $262.63   $262.65   $262.60  
  Purchase #6 $22.84   13.751%   $25.9807   $25.98   $26.00   $26.00  
  Purchase #7 $50.30   8.554%   $54.6027   $54.60   $54.60   $54.60  
  7 purchase totals = $861.96       $942.1673   $942.16   $942.20   $942.10