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 $197.39   3.130%   $203.5683   $203.57   $203.55   $203.60  
  Purchase #2 $149.66   7.379%   $160.7034   $160.70   $160.70   $160.70  
  Purchase #3 $163.54   10.680%   $181.0061   $181.01   $181.00   $181.00  
  Purchase #4 $153.77   10.398%   $169.759   $169.76   $169.75   $169.80  
  Purchase #5 $227.66   4.371%   $237.611   $237.61   $237.60   $237.60  
  Purchase #6 $9.31   3.847%   $9.6682   $9.67   $9.65   $9.70  
  Purchase #7 $226.30   3.166%   $233.4647   $233.46   $233.45   $233.50  
  7 purchase totals = $1,127.63       $1,195.7807   $1,195.78   $1,195.70   $1,195.90