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 $204.67   12.196%   $229.6316   $229.63   $229.65   $229.60  
  Purchase #2 $215.48   12.508%   $242.4322   $242.43   $242.45   $242.40  
  Purchase #3 $24.62   6.507%   $26.222   $26.22   $26.20   $26.20  
  Purchase #4 $84.81   4.455%   $88.5883   $88.59   $88.60   $88.60  
  Purchase #5 $183.88   6.182%   $195.2475   $195.25   $195.25   $195.20  
  Purchase #6 $35.64   7.560%   $38.3344   $38.33   $38.35   $38.30  
  Purchase #7 $242.51   5.470%   $255.7753   $255.78   $255.80   $255.80  
  7 purchase totals = $991.61       $1,076.2313   $1,076.23   $1,076.30   $1,076.10