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 $78.94   9.617%   $86.5317   $86.53   $86.55   $86.50  
  Purchase #2 $248.34   12.645%   $279.7426   $279.74   $279.75   $279.70  
  Purchase #3 $91.96   13.537%   $104.4086   $104.41   $104.40   $104.40  
  Purchase #4 $174.42   7.467%   $187.4439   $187.44   $187.45   $187.40  
  Purchase #5 $58.87   5.251%   $61.9613   $61.96   $61.95   $62.00  
  Purchase #6 $28.36   12.845%   $32.0028   $32.00   $32.00   $32.00  
  Purchase #7 $9.51   7.755%   $10.2475   $10.25   $10.25   $10.20  
  7 purchase totals = $690.40       $762.3384   $762.33   $762.35   $762.20