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 $101.47   11.728%   $113.3704   $113.37   $113.35   $113.40  
  Purchase #2 $26.65   9.656%   $29.2233   $29.22   $29.20   $29.20  
  Purchase #3 $177.56   7.776%   $191.3671   $191.37   $191.35   $191.40  
  Purchase #4 $148.51   7.191%   $159.1894   $159.19   $159.20   $159.20  
  Purchase #5 $65.79   5.480%   $69.3953   $69.40   $69.40   $69.40  
  Purchase #6 $219.52   3.831%   $227.9298   $227.93   $227.95   $227.90  
  Purchase #7 $221.88   4.507%   $231.8801   $231.88   $231.90   $231.90  
  7 purchase totals = $961.38       $1,022.3554   $1,022.36   $1,022.35   $1,022.40