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 $167.63   10.144%   $184.6344   $184.63   $184.65   $184.60  
  Purchase #2 $243.89   13.216%   $276.1225   $276.12   $276.10   $276.10  
  Purchase #3 $176.46   13.725%   $200.6791   $200.68   $200.70   $200.70  
  Purchase #4 $245.90   9.168%   $268.4441   $268.44   $268.45   $268.40  
  Purchase #5 $204.61   6.551%   $218.014   $218.01   $218.00   $218.00  
  Purchase #6 $102.52   7.618%   $110.33   $110.33   $110.35   $110.30  
  Purchase #7 $227.38   4.778%   $238.2442   $238.24   $238.25   $238.20  
  7 purchase totals = $1,368.39       $1,496.4683   $1,496.45   $1,496.50   $1,496.30