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 $62.47   12.166%   $70.0701   $70.07   $70.05   $70.10  
  Purchase #2 $196.34   3.419%   $203.0529   $203.05   $203.05   $203.10  
  Purchase #3 $200.58   7.129%   $214.8793   $214.88   $214.90   $214.90  
  Purchase #4 $89.27   11.224%   $99.2897   $99.29   $99.30   $99.30  
  Purchase #5 $92.56   12.499%   $104.1291   $104.13   $104.15   $104.10  
  Purchase #6 $14.45   13.193%   $16.3564   $16.36   $16.35   $16.40  
  Purchase #7 $81.96   12.860%   $92.5001   $92.50   $92.50   $92.50  
  7 purchase totals = $737.63       $800.2776   $800.28   $800.30   $800.40