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 $56.58   3.724%   $58.687   $58.69   $58.70   $58.70  
  Purchase #2 $238.84   8.496%   $259.1318   $259.13   $259.15   $259.10  
  Purchase #3 $118.68   12.629%   $133.6681   $133.67   $133.65   $133.70  
  Purchase #4 $216.35   11.261%   $240.7132   $240.71   $240.70   $240.70  
  Purchase #5 $250.97   9.552%   $274.9427   $274.94   $274.95   $274.90  
  Purchase #6 $149.91   11.668%   $167.4015   $167.40   $167.40   $167.40  
  Purchase #7 $198.51   7.850%   $214.093   $214.09   $214.10   $214.10  
  7 purchase totals = $1,229.84       $1,348.6373   $1,348.63   $1,348.65   $1,348.60