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 $60.86   7.556%   $65.4586   $65.46   $65.45   $65.50  
  Purchase #2 $48.94   9.673%   $53.674   $53.67   $53.65   $53.70  
  Purchase #3 $23.63   11.775%   $26.4124   $26.41   $26.40   $26.40  
  Purchase #4 $197.85   6.123%   $209.9644   $209.96   $209.95   $210.00  
  Purchase #5 $176.58   5.601%   $186.4702   $186.47   $186.45   $186.50  
  Purchase #6 $165.60   12.461%   $186.2354   $186.24   $186.25   $186.20  
  Purchase #7 $30.52   9.408%   $33.3913   $33.39   $33.40   $33.40  
  7 purchase totals = $703.98       $761.6063   $761.60   $761.55   $761.70