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 $227.90   5.755%   $241.0156   $241.02   $241.00   $241.00  
  Purchase #2 $169.68   13.103%   $191.9132   $191.91   $191.90   $191.90  
  Purchase #3 $64.78   4.612%   $67.7677   $67.77   $67.75   $67.80  
  Purchase #4 $148.91   4.506%   $155.6199   $155.62   $155.60   $155.60  
  Purchase #5 $181.25   4.778%   $189.9101   $189.91   $189.90   $189.90  
  Purchase #6 $147.98   6.163%   $157.1   $157.10   $157.10   $157.10  
  Purchase #7 $187.45   8.212%   $202.8434   $202.84   $202.85   $202.80  
  7 purchase totals = $1,127.95       $1,206.1699   $1,206.17   $1,206.10   $1,206.10