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 $165.37   10.601%   $182.9009   $182.90   $182.90   $182.90  
  Purchase #2 $175.71   6.236%   $186.6673   $186.67   $186.65   $186.70  
  Purchase #3 $53.61   11.443%   $59.7446   $59.74   $59.75   $59.70  
  Purchase #4 $235.58   6.151%   $250.0705   $250.07   $250.05   $250.10  
  Purchase #5 $201.65   9.654%   $221.1173   $221.12   $221.10   $221.10  
  Purchase #6 $112.72   11.503%   $125.6862   $125.69   $125.70   $125.70  
  Purchase #7 $214.48   6.618%   $228.6743   $228.67   $228.65   $228.70  
  7 purchase totals = $1,159.12       $1,254.8611   $1,254.86   $1,254.80   $1,254.90