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 $225.42   12.559%   $253.7305   $253.73   $253.75   $253.70  
  Purchase #2 $130.63   11.157%   $145.2044   $145.20   $145.20   $145.20  
  Purchase #3 $189.78   3.426%   $196.2819   $196.28   $196.30   $196.30  
  Purchase #4 $204.68   11.771%   $228.7729   $228.77   $228.75   $228.80  
  Purchase #5 $144.75   13.146%   $163.7788   $163.78   $163.80   $163.80  
  Purchase #6 $68.40   13.633%   $77.725   $77.73   $77.75   $77.70  
  Purchase #7 $160.29   12.717%   $180.6741   $180.67   $180.65   $180.70  
  7 purchase totals = $1,123.95       $1,246.1676   $1,246.16   $1,246.20   $1,246.20