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 $165.66   6.817%   $176.953   $176.95   $176.95   $177.00  
  Purchase #2 $103.73   8.868%   $112.9288   $112.93   $112.95   $112.90  
  Purchase #3 $245.34   7.317%   $263.2915   $263.29   $263.30   $263.30  
  Purchase #4 $210.56   13.749%   $239.5099   $239.51   $239.50   $239.50  
  Purchase #5 $89.32   5.253%   $94.012   $94.01   $94.00   $94.00  
  Purchase #6 $102.86   12.820%   $116.0467   $116.05   $116.05   $116.00  
  Purchase #7 $78.98   8.384%   $85.6017   $85.60   $85.60   $85.60  
  7 purchase totals = $996.45       $1,088.3436   $1,088.34   $1,088.35   $1,088.30