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 $61.37   7.516%   $65.9826   $65.98   $66.00   $66.00  
  Purchase #2 $219.77   4.118%   $228.8201   $228.82   $228.80   $228.80  
  Purchase #3 $83.87   7.346%   $90.0311   $90.03   $90.05   $90.00  
  Purchase #4 $68.59   8.867%   $74.6719   $74.67   $74.65   $74.70  
  Purchase #5 $190.26   4.412%   $198.6543   $198.65   $198.65   $198.70  
  Purchase #6 $16.99   9.256%   $18.5626   $18.56   $18.55   $18.60  
  Purchase #7 $119.78   6.165%   $127.1644   $127.16   $127.15   $127.20  
  7 purchase totals = $760.63       $803.8870   $803.87   $803.85   $804.00