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 $32.32   12.486%   $36.3555   $36.36   $36.35   $36.40  
  Purchase #2 $60.57   6.460%   $64.4828   $64.48   $64.50   $64.50  
  Purchase #3 $44.29   3.772%   $45.9606   $45.96   $45.95   $46.00  
  Purchase #4 $242.41   9.737%   $266.0135   $266.01   $266.00   $266.00  
  Purchase #5 $218.91   13.379%   $248.198   $248.20   $248.20   $248.20  
  Purchase #6 $192.55   5.306%   $202.7667   $202.77   $202.75   $202.80  
  Purchase #7 $85.86   3.104%   $88.5251   $88.53   $88.55   $88.50  
  7 purchase totals = $876.91       $952.3022   $952.31   $952.30   $952.40