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 $187.72   8.859%   $204.3501   $204.35   $204.35   $204.40  
  Purchase #2 $68.28   8.611%   $74.1596   $74.16   $74.15   $74.20  
  Purchase #3 $226.43   7.214%   $242.7647   $242.76   $242.75   $242.80  
  Purchase #4 $148.36   12.687%   $167.1824   $167.18   $167.20   $167.20  
  Purchase #5 $114.87   12.284%   $128.9806   $128.98   $129.00   $129.00  
  Purchase #6 $169.55   8.477%   $183.9228   $183.92   $183.90   $183.90  
  Purchase #7 $179.72   11.745%   $200.8281   $200.83   $200.85   $200.80  
  7 purchase totals = $1,094.93       $1,202.1883   $1,202.18   $1,202.20   $1,202.30