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 $195.93   12.585%   $220.5878   $220.59   $220.60   $220.60  
  Purchase #2 $207.79   5.413%   $219.0377   $219.04   $219.05   $219.00  
  Purchase #3 $160.96   10.526%   $177.9026   $177.90   $177.90   $177.90  
  Purchase #4 $12.77   11.559%   $14.2461   $14.25   $14.25   $14.20  
  Purchase #5 $209.72   7.420%   $225.2812   $225.28   $225.30   $225.30  
  Purchase #6 $101.86   3.358%   $105.2805   $105.28   $105.30   $105.30  
  Purchase #7 $54.89   10.408%   $60.603   $60.60   $60.60   $60.60  
  7 purchase totals = $943.92       $1,022.9389   $1,022.94   $1,023.00   $1,022.90