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 $208.29   13.706%   $236.8382   $236.84   $236.85   $236.80  
  Purchase #2 $53.87   13.478%   $61.1306   $61.13   $61.15   $61.10  
  Purchase #3 $62.67   10.279%   $69.1118   $69.11   $69.10   $69.10  
  Purchase #4 $13.76   8.524%   $14.9329   $14.93   $14.95   $14.90  
  Purchase #5 $71.40   11.538%   $79.6381   $79.64   $79.65   $79.60  
  Purchase #6 $209.31   12.545%   $235.5679   $235.57   $235.55   $235.60  
  Purchase #7 $168.37   9.279%   $183.9931   $183.99   $184.00   $184.00  
  7 purchase totals = $787.67       $881.2126   $881.21   $881.25   $881.10