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 $229.49   6.404%   $244.1865   $244.19   $244.20   $244.20  
  Purchase #2 $166.79   5.304%   $175.6365   $175.64   $175.65   $175.60  
  Purchase #3 $74.92   8.390%   $81.2058   $81.21   $81.20   $81.20  
  Purchase #4 $149.40   9.203%   $163.1493   $163.15   $163.15   $163.10  
  Purchase #5 $52.97   5.254%   $55.753   $55.75   $55.75   $55.80  
  Purchase #6 $27.84   7.810%   $30.0143   $30.01   $30.00   $30.00  
  Purchase #7 $179.81   4.150%   $187.2721   $187.27   $187.25   $187.30  
  7 purchase totals = $881.22       $937.2175   $937.22   $937.20   $937.20