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 $107.95   4.706%   $113.0301   $113.03   $113.05   $113.00  
  Purchase #2 $151.67   5.257%   $159.6433   $159.64   $159.65   $159.60  
  Purchase #3 $191.42   3.619%   $198.3475   $198.35   $198.35   $198.30  
  Purchase #4 $102.67   6.636%   $109.4832   $109.48   $109.50   $109.50  
  Purchase #5 $129.94   4.153%   $135.3364   $135.34   $135.35   $135.30  
  Purchase #6 $45.63   6.392%   $48.5467   $48.55   $48.55   $48.50  
  Purchase #7 $237.59   9.317%   $259.7263   $259.73   $259.75   $259.70  
  7 purchase totals = $966.87       $1,024.1135   $1,024.12   $1,024.20   $1,023.90