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 $56.49   13.295%   $64.0003   $64.00   $64.00   $64.00  
  Purchase #2 $78.69   4.192%   $81.9887   $81.99   $82.00   $82.00  
  Purchase #3 $148.97   11.408%   $165.9645   $165.96   $165.95   $166.00  
  Purchase #4 $179.84   12.466%   $202.2589   $202.26   $202.25   $202.30  
  Purchase #5 $178.98   7.447%   $192.3086   $192.31   $192.30   $192.30  
  Purchase #6 $93.83   13.543%   $106.5374   $106.54   $106.55   $106.50  
  Purchase #7 $192.95   13.723%   $219.4285   $219.43   $219.45   $219.40  
  7 purchase totals = $929.75       $1,032.4869   $1,032.49   $1,032.50   $1,032.50