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 $244.60   6.370%   $260.181   $260.18   $260.20   $260.20  
  Purchase #2 $137.44   13.223%   $155.6137   $155.61   $155.60   $155.60  
  Purchase #3 $95.79   8.376%   $103.8134   $103.81   $103.80   $103.80  
  Purchase #4 $57.54   13.447%   $65.2774   $65.28   $65.30   $65.30  
  Purchase #5 $227.65   10.251%   $250.9864   $250.99   $251.00   $251.00  
  Purchase #6 $198.45   10.316%   $218.9221   $218.92   $218.90   $218.90  
  Purchase #7 $30.34   11.789%   $33.9168   $33.92   $33.90   $33.90  
  7 purchase totals = $991.81       $1,088.7108   $1,088.71   $1,088.70   $1,088.70