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 $214.88   12.116%   $240.9149   $240.91   $240.90   $240.90  
  Purchase #2 $38.84   6.478%   $41.3561   $41.36   $41.35   $41.40  
  Purchase #3 $41.51   8.235%   $44.9283   $44.93   $44.95   $44.90  
  Purchase #4 $216.72   5.551%   $228.7501   $228.75   $228.75   $228.80  
  Purchase #5 $78.70   13.515%   $89.3363   $89.34   $89.35   $89.30  
  Purchase #6 $191.86   6.161%   $203.6805   $203.68   $203.70   $203.70  
  Purchase #7 $179.77   11.380%   $200.2278   $200.23   $200.25   $200.20  
  7 purchase totals = $962.28       $1,049.1940   $1,049.20   $1,049.25   $1,049.20