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 $162.73   11.793%   $181.9207   $181.92   $181.90   $181.90  
  Purchase #2 $208.81   11.283%   $232.37   $232.37   $232.35   $232.40  
  Purchase #3 $192.81   6.213%   $204.7893   $204.79   $204.80   $204.80  
  Purchase #4 $129.27   11.443%   $144.0624   $144.06   $144.05   $144.10  
  Purchase #5 $188.28   9.196%   $205.5942   $205.59   $205.60   $205.60  
  Purchase #6 $221.32   5.387%   $233.2425   $233.24   $233.25   $233.20  
  Purchase #7 $68.48   5.478%   $72.2313   $72.23   $72.25   $72.20  
  7 purchase totals = $1,171.70       $1,274.2104   $1,274.20   $1,274.20   $1,274.20