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 $60.31   7.286%   $64.7042   $64.70   $64.70   $64.70  
  Purchase #2 $17.85   10.859%   $19.7883   $19.79   $19.80   $19.80  
  Purchase #3 $220.34   5.712%   $232.9258   $232.93   $232.95   $232.90  
  Purchase #4 $27.25   12.419%   $30.6342   $30.63   $30.65   $30.60  
  Purchase #5 $209.42   4.363%   $218.557   $218.56   $218.55   $218.60  
  Purchase #6 $147.62   6.482%   $157.1887   $157.19   $157.20   $157.20  
  Purchase #7 $23.91   11.379%   $26.6307   $26.63   $26.65   $26.60  
  7 purchase totals = $706.70       $750.4289   $750.43   $750.50   $750.40