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 $65.83   12.180%   $73.8481   $73.85   $73.85   $73.80  
  Purchase #2 $60.83   7.588%   $65.4458   $65.45   $65.45   $65.40  
  Purchase #3 $136.94   7.106%   $146.671   $146.67   $146.65   $146.70  
  Purchase #4 $197.45   4.807%   $206.9414   $206.94   $206.95   $206.90  
  Purchase #5 $84.94   6.572%   $90.5223   $90.52   $90.50   $90.50  
  Purchase #6 $195.88   12.817%   $220.9859   $220.99   $221.00   $221.00  
  Purchase #7 $50.66   6.232%   $53.8171   $53.82   $53.80   $53.80  
  7 purchase totals = $792.53       $858.2316   $858.24   $858.20   $858.10