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 $69.98   8.539%   $75.9556   $75.96   $75.95   $76.00  
  Purchase #2 $246.71   6.866%   $263.6491   $263.65   $263.65   $263.60  
  Purchase #3 $66.27   5.718%   $70.0593   $70.06   $70.05   $70.10  
  Purchase #4 $34.74   6.231%   $36.9046   $36.90   $36.90   $36.90  
  Purchase #5 $32.58   11.175%   $36.2208   $36.22   $36.20   $36.20  
  Purchase #6 $114.30   3.146%   $117.8959   $117.90   $117.90   $117.90  
  Purchase #7 $17.32   10.459%   $19.1315   $19.13   $19.15   $19.10  
  7 purchase totals = $581.90       $619.8168   $619.82   $619.80   $619.80