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 $84.83   4.622%   $88.7508   $88.75   $88.75   $88.80  
  Purchase #2 $51.54   7.272%   $55.288   $55.29   $55.30   $55.30  
  Purchase #3 $169.58   13.464%   $192.4123   $192.41   $192.40   $192.40  
  Purchase #4 $23.88   11.194%   $26.5531   $26.55   $26.55   $26.60  
  Purchase #5 $250.58   9.197%   $273.6258   $273.63   $273.65   $273.60  
  Purchase #6 $164.81   13.205%   $186.5732   $186.57   $186.55   $186.60  
  Purchase #7 $183.52   8.869%   $199.7964   $199.80   $199.80   $199.80  
  7 purchase totals = $928.74       $1,022.9996   $1,023.00   $1,023.00   $1,023.10