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 $132.98   13.562%   $151.0147   $151.01   $151.00   $151.00  
  Purchase #2 $72.48   11.396%   $80.7398   $80.74   $80.75   $80.70  
  Purchase #3 $15.49   11.750%   $17.3101   $17.31   $17.30   $17.30  
  Purchase #4 $61.62   13.797%   $70.1217   $70.12   $70.10   $70.10  
  Purchase #5 $214.28   12.543%   $241.1571   $241.16   $241.15   $241.20  
  Purchase #6 $23.41   13.286%   $26.5203   $26.52   $26.50   $26.50  
  Purchase #7 $187.91   11.327%   $209.1946   $209.19   $209.20   $209.20  
  7 purchase totals = $708.17       $796.0583   $796.05   $796.00   $796.00