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 $249.48   11.237%   $277.5141   $277.51   $277.50   $277.50  
  Purchase #2 $219.63   8.661%   $238.6522   $238.65   $238.65   $238.70  
  Purchase #3 $55.29   4.484%   $57.7692   $57.77   $57.75   $57.80  
  Purchase #4 $215.35   6.217%   $228.7383   $228.74   $228.75   $228.70  
  Purchase #5 $224.85   3.171%   $231.98   $231.98   $232.00   $232.00  
  Purchase #6 $108.39   9.112%   $118.2665   $118.27   $118.25   $118.30  
  Purchase #7 $5.49   4.340%   $5.7283   $5.73   $5.75   $5.70  
  7 purchase totals = $1,078.48       $1,158.6486   $1,158.65   $1,158.65   $1,158.70