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 $106.41   12.821%   $120.0528   $120.05   $120.05   $120.10  
  Purchase #2 $244.45   11.722%   $273.1044   $273.10   $273.10   $273.10  
  Purchase #3 $189.82   4.378%   $198.1303   $198.13   $198.15   $198.10  
  Purchase #4 $236.26   13.469%   $268.0819   $268.08   $268.10   $268.10  
  Purchase #5 $45.25   11.184%   $50.3108   $50.31   $50.30   $50.30  
  Purchase #6 $15.44   4.546%   $16.1419   $16.14   $16.15   $16.10  
  Purchase #7 $174.35   13.166%   $197.3049   $197.30   $197.30   $197.30  
  7 purchase totals = $1,011.98       $1,123.1270   $1,123.11   $1,123.15   $1,123.10