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 $207.82   6.714%   $221.773   $221.77   $221.75   $221.80  
  Purchase #2 $159.65   8.337%   $172.96   $172.96   $172.95   $173.00  
  Purchase #3 $248.65   10.452%   $274.6389   $274.64   $274.65   $274.60  
  Purchase #4 $126.98   11.205%   $141.2081   $141.21   $141.20   $141.20  
  Purchase #5 $132.77   7.580%   $142.834   $142.83   $142.85   $142.80  
  Purchase #6 $178.76   12.320%   $200.7832   $200.78   $200.80   $200.80  
  Purchase #7 $37.66   10.354%   $41.5593   $41.56   $41.55   $41.60  
  7 purchase totals = $1,092.29       $1,195.7565   $1,195.75   $1,195.75   $1,195.80