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 $193.28   6.167%   $205.1996   $205.20   $205.20   $205.20  
  Purchase #2 $248.27   6.600%   $264.6558   $264.66   $264.65   $264.70  
  Purchase #3 $243.38   9.735%   $267.073   $267.07   $267.05   $267.10  
  Purchase #4 $72.30   5.520%   $76.291   $76.29   $76.30   $76.30  
  Purchase #5 $24.55   10.441%   $27.1133   $27.11   $27.10   $27.10  
  Purchase #6 $75.65   10.502%   $83.5948   $83.59   $83.60   $83.60  
  Purchase #7 $76.93   4.776%   $80.6042   $80.60   $80.60   $80.60  
  7 purchase totals = $934.36       $1,004.5317   $1,004.52   $1,004.50   $1,004.60