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 $186.47   9.697%   $204.552   $204.55   $204.55   $204.60  
  Purchase #2 $227.75   12.784%   $256.8656   $256.87   $256.85   $256.90  
  Purchase #3 $111.45   5.833%   $117.9509   $117.95   $117.95   $118.00  
  Purchase #4 $34.59   5.113%   $36.3586   $36.36   $36.35   $36.40  
  Purchase #5 $64.98   12.676%   $73.2169   $73.22   $73.20   $73.20  
  Purchase #6 $243.68   4.548%   $254.7626   $254.76   $254.75   $254.80  
  Purchase #7 $148.50   3.618%   $153.8727   $153.87   $153.85   $153.90  
  7 purchase totals = $1,017.42       $1,097.5793   $1,097.58   $1,097.50   $1,097.80