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 $53.96   8.308%   $58.443   $58.44   $58.45   $58.40  
  Purchase #2 $214.48   8.586%   $232.8953   $232.90   $232.90   $232.90  
  Purchase #3 $25.37   3.269%   $26.1993   $26.20   $26.20   $26.20  
  Purchase #4 $56.45   11.578%   $62.9858   $62.99   $63.00   $63.00  
  Purchase #5 $105.70   11.745%   $118.1145   $118.11   $118.10   $118.10  
  Purchase #6 $118.25   10.574%   $130.7538   $130.75   $130.75   $130.80  
  Purchase #7 $209.93   13.620%   $238.5225   $238.52   $238.50   $238.50  
  7 purchase totals = $784.14       $867.9142   $867.91   $867.90   $867.90