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 $69.79   5.440%   $73.5866   $73.59   $73.60   $73.60  
  Purchase #2 $117.29   6.234%   $124.6019   $124.60   $124.60   $124.60  
  Purchase #3 $165.84   9.872%   $182.2117   $182.21   $182.20   $182.20  
  Purchase #4 $144.97   6.758%   $154.7671   $154.77   $154.75   $154.80  
  Purchase #5 $31.88   4.409%   $33.2856   $33.29   $33.30   $33.30  
  Purchase #6 $210.84   5.525%   $222.4889   $222.49   $222.50   $222.50  
  Purchase #7 $64.99   8.228%   $70.3374   $70.34   $70.35   $70.30  
  7 purchase totals = $805.60       $861.2792   $861.29   $861.30   $861.30