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 $227.54   11.582%   $253.8937   $253.89   $253.90   $253.90  
  Purchase #2 $189.58   12.178%   $212.6671   $212.67   $212.65   $212.70  
  Purchase #3 $185.96   4.814%   $194.9121   $194.91   $194.90   $194.90  
  Purchase #4 $101.64   6.261%   $108.0037   $108.00   $108.00   $108.00  
  Purchase #5 $92.48   6.273%   $98.2813   $98.28   $98.30   $98.30  
  Purchase #6 $96.93   4.724%   $101.509   $101.51   $101.50   $101.50  
  Purchase #7 $187.93   8.658%   $204.201   $204.20   $204.20   $204.20  
  7 purchase totals = $1,082.06       $1,173.4679   $1,173.46   $1,173.45   $1,173.50