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 $68.99   6.655%   $73.5813   $73.58   $73.60   $73.60  
  Purchase #2 $110.98   4.640%   $116.1295   $116.13   $116.15   $116.10  
  Purchase #3 $96.79   11.613%   $108.0302   $108.03   $108.05   $108.00  
  Purchase #4 $82.31   7.269%   $88.2931   $88.29   $88.30   $88.30  
  Purchase #5 $147.67   12.282%   $165.8068   $165.81   $165.80   $165.80  
  Purchase #6 $8.82   11.500%   $9.8343   $9.83   $9.85   $9.80  
  Purchase #7 $188.54   5.203%   $198.3497   $198.35   $198.35   $198.30  
  7 purchase totals = $704.10       $760.0249   $760.02   $760.10   $759.90