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 $249.54   9.474%   $273.1814   $273.18   $273.20   $273.20  
  Purchase #2 $223.40   5.650%   $236.0221   $236.02   $236.00   $236.00  
  Purchase #3 $27.27   3.454%   $28.2119   $28.21   $28.20   $28.20  
  Purchase #4 $85.92   11.568%   $95.8592   $95.86   $95.85   $95.90  
  Purchase #5 $197.57   13.215%   $223.6789   $223.68   $223.70   $223.70  
  Purchase #6 $41.81   5.192%   $43.9808   $43.98   $44.00   $44.00  
  Purchase #7 $106.87   6.369%   $113.6766   $113.68   $113.70   $113.70  
  7 purchase totals = $932.38       $1,014.6109   $1,014.61   $1,014.65   $1,014.70