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 $202.69   11.538%   $226.0764   $226.08   $226.10   $226.10  
  Purchase #2 $83.42   4.301%   $87.0079   $87.01   $87.00   $87.00  
  Purchase #3 $163.38   7.646%   $175.872   $175.87   $175.85   $175.90  
  Purchase #4 $163.42   6.861%   $174.6322   $174.63   $174.65   $174.60  
  Purchase #5 $241.88   6.685%   $258.0497   $258.05   $258.05   $258.00  
  Purchase #6 $56.93   6.363%   $60.5525   $60.55   $60.55   $60.60  
  Purchase #7 $138.37   4.584%   $144.7129   $144.71   $144.70   $144.70  
  7 purchase totals = $1,050.09       $1,126.9036   $1,126.90   $1,126.90   $1,126.90