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 $239.63   10.224%   $264.1298   $264.13   $264.15   $264.10  
  Purchase #2 $224.69   3.521%   $232.6013   $232.60   $232.60   $232.60  
  Purchase #3 $25.31   11.789%   $28.2938   $28.29   $28.30   $28.30  
  Purchase #4 $71.65   3.570%   $74.2079   $74.21   $74.20   $74.20  
  Purchase #5 $238.92   10.343%   $263.6315   $263.63   $263.65   $263.60  
  Purchase #6 $176.39   13.783%   $200.7018   $200.70   $200.70   $200.70  
  Purchase #7 $149.43   10.866%   $165.6671   $165.67   $165.65   $165.70  
  7 purchase totals = $1,126.02       $1,229.2332   $1,229.23   $1,229.25   $1,229.20