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 $88.53   6.487%   $94.2729   $94.27   $94.25   $94.30  
  Purchase #2 $219.57   5.543%   $231.7408   $231.74   $231.75   $231.70  
  Purchase #3 $93.29   11.450%   $103.9717   $103.97   $103.95   $104.00  
  Purchase #4 $166.28   11.414%   $185.2592   $185.26   $185.25   $185.30  
  Purchase #5 $146.36   7.281%   $157.0165   $157.02   $157.00   $157.00  
  Purchase #6 $221.54   5.415%   $233.5364   $233.54   $233.55   $233.50  
  Purchase #7 $71.82   11.856%   $80.335   $80.34   $80.35   $80.30  
  7 purchase totals = $1,007.39       $1,086.1325   $1,086.14   $1,086.10   $1,086.10