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 $59.60   6.627%   $63.5497   $63.55   $63.55   $63.50  
  Purchase #2 $131.61   13.814%   $149.7906   $149.79   $149.80   $149.80  
  Purchase #3 $92.62   11.316%   $103.1009   $103.10   $103.10   $103.10  
  Purchase #4 $71.82   12.364%   $80.6998   $80.70   $80.70   $80.70  
  Purchase #5 $31.36   11.301%   $34.904   $34.90   $34.90   $34.90  
  Purchase #6 $174.74   6.500%   $186.0981   $186.10   $186.10   $186.10  
  Purchase #7 $138.65   5.777%   $146.6598   $146.66   $146.65   $146.70  
  7 purchase totals = $700.40       $764.8029   $764.80   $764.80   $764.80