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 $54.77   9.796%   $60.1353   $60.14   $60.15   $60.10  
  Purchase #2 $220.62   4.170%   $229.8199   $229.82   $229.80   $229.80  
  Purchase #3 $101.30   6.235%   $107.6161   $107.62   $107.60   $107.60  
  Purchase #4 $52.60   12.615%   $59.2355   $59.24   $59.25   $59.20  
  Purchase #5 $232.83   10.587%   $257.4797   $257.48   $257.50   $257.50  
  Purchase #6 $38.37   3.345%   $39.6535   $39.65   $39.65   $39.70  
  Purchase #7 $37.37   10.257%   $41.203   $41.20   $41.20   $41.20  
  7 purchase totals = $737.86       $795.1430   $795.15   $795.15   $795.10