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 $68.79   12.681%   $77.5133   $77.51   $77.50   $77.50  
  Purchase #2 $218.37   3.416%   $225.8295   $225.83   $225.85   $225.80  
  Purchase #3 $88.85   9.384%   $97.1877   $97.19   $97.20   $97.20  
  Purchase #4 $209.53   11.137%   $232.8654   $232.87   $232.85   $232.90  
  Purchase #5 $189.93   11.102%   $211.016   $211.02   $211.00   $211.00  
  Purchase #6 $198.48   7.454%   $213.2747   $213.27   $213.25   $213.30  
  Purchase #7 $246.38   12.654%   $277.5569   $277.56   $277.55   $277.60  
  7 purchase totals = $1,220.33       $1,335.2435   $1,335.25   $1,335.20   $1,335.30