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 $209.96   11.115%   $233.2971   $233.30   $233.30   $233.30  
  Purchase #2 $184.37   3.779%   $191.3373   $191.34   $191.35   $191.30  
  Purchase #3 $59.71   5.244%   $62.8412   $62.84   $62.85   $62.80  
  Purchase #4 $236.64   7.661%   $254.769   $254.77   $254.75   $254.80  
  Purchase #5 $220.30   7.609%   $237.0626   $237.06   $237.05   $237.10  
  Purchase #6 $126.34   8.696%   $137.3265   $137.33   $137.35   $137.30  
  Purchase #7 $119.75   7.114%   $128.269   $128.27   $128.25   $128.30  
  7 purchase totals = $1,157.07       $1,244.9027   $1,244.91   $1,244.90   $1,244.90