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 $204.44   11.703%   $228.3656   $228.37   $228.35   $228.40  
  Purchase #2 $175.44   12.654%   $197.6402   $197.64   $197.65   $197.60  
  Purchase #3 $225.27   7.822%   $242.8906   $242.89   $242.90   $242.90  
  Purchase #4 $110.26   7.453%   $118.4777   $118.48   $118.50   $118.50  
  Purchase #5 $196.32   6.389%   $208.8629   $208.86   $208.85   $208.90  
  Purchase #6 $58.37   3.591%   $60.4661   $60.47   $60.45   $60.50  
  Purchase #7 $21.57   11.267%   $24.0003   $24.00   $24.00   $24.00  
  7 purchase totals = $991.67       $1,080.7034   $1,080.71   $1,080.70   $1,080.80