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 $41.69   11.355%   $46.4239   $46.42   $46.40   $46.40  
  Purchase #2 $165.97   6.767%   $177.2012   $177.20   $177.20   $177.20  
  Purchase #3 $143.67   9.666%   $157.5571   $157.56   $157.55   $157.60  
  Purchase #4 $24.96   4.252%   $26.0213   $26.02   $26.00   $26.00  
  Purchase #5 $145.47   10.429%   $160.6411   $160.64   $160.65   $160.60  
  Purchase #6 $192.86   8.782%   $209.797   $209.80   $209.80   $209.80  
  Purchase #7 $149.60   7.693%   $161.1087   $161.11   $161.10   $161.10  
  7 purchase totals = $864.22       $938.7503   $938.75   $938.70   $938.70