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 $200.40   12.794%   $226.0392   $226.04   $226.05   $226.00  
  Purchase #2 $51.96   4.602%   $54.3512   $54.35   $54.35   $54.40  
  Purchase #3 $241.95   13.224%   $273.9455   $273.95   $273.95   $273.90  
  Purchase #4 $58.63   7.288%   $62.903   $62.90   $62.90   $62.90  
  Purchase #5 $88.40   9.392%   $96.7025   $96.70   $96.70   $96.70  
  Purchase #6 $196.32   10.541%   $217.0141   $217.01   $217.00   $217.00  
  Purchase #7 $74.45   4.220%   $77.5918   $77.59   $77.60   $77.60  
  7 purchase totals = $912.11       $1,008.5473   $1,008.54   $1,008.55   $1,008.50