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 $103.51   4.201%   $107.8585   $107.86   $107.85   $107.90  
  Purchase #2 $127.64   11.135%   $141.8527   $141.85   $141.85   $141.90  
  Purchase #3 $205.28   13.409%   $232.806   $232.81   $232.80   $232.80  
  Purchase #4 $48.28   7.669%   $51.9826   $51.98   $52.00   $52.00  
  Purchase #5 $57.44   12.649%   $64.7056   $64.71   $64.70   $64.70  
  Purchase #6 $202.64   13.503%   $230.0025   $230.00   $230.00   $230.00  
  Purchase #7 $204.60   5.420%   $215.6893   $215.69   $215.70   $215.70  
  7 purchase totals = $949.39       $1,044.8972   $1,044.90   $1,044.90   $1,045.00