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 $241.76   7.555%   $260.025   $260.03   $260.05   $260.00  
  Purchase #2 $198.59   6.716%   $211.9273   $211.93   $211.95   $211.90  
  Purchase #3 $184.98   12.801%   $208.6593   $208.66   $208.65   $208.70  
  Purchase #4 $125.36   8.135%   $135.558   $135.56   $135.55   $135.60  
  Purchase #5 $213.50   11.858%   $238.8168   $238.82   $238.80   $238.80  
  Purchase #6 $15.26   3.364%   $15.7733   $15.77   $15.75   $15.80  
  Purchase #7 $160.33   13.250%   $181.5737   $181.57   $181.55   $181.60  
  7 purchase totals = $1,139.78       $1,252.3334   $1,252.34   $1,252.30   $1,252.40