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 $146.72   5.574%   $154.8982   $154.90   $154.90   $154.90  
  Purchase #2 $187.51   8.603%   $203.6415   $203.64   $203.65   $203.60  
  Purchase #3 $244.63   9.724%   $268.4178   $268.42   $268.40   $268.40  
  Purchase #4 $21.70   10.290%   $23.9329   $23.93   $23.95   $23.90  
  Purchase #5 $135.46   11.534%   $151.084   $151.08   $151.10   $151.10  
  Purchase #6 $160.40   4.125%   $167.0165   $167.02   $167.00   $167.00  
  Purchase #7 $213.85   6.334%   $227.3953   $227.40   $227.40   $227.40  
  7 purchase totals = $1,110.27       $1,196.3862   $1,196.39   $1,196.40   $1,196.30