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 $179.81   9.245%   $196.4334   $196.43   $196.45   $196.40  
  Purchase #2 $137.75   9.374%   $150.6627   $150.66   $150.65   $150.70  
  Purchase #3 $250.63   6.732%   $267.5024   $267.50   $267.50   $267.50  
  Purchase #4 $84.38   8.598%   $91.635   $91.64   $91.65   $91.60  
  Purchase #5 $112.26   7.872%   $121.0971   $121.10   $121.10   $121.10  
  Purchase #6 $172.59   12.678%   $194.471   $194.47   $194.45   $194.50  
  Purchase #7 $35.96   8.419%   $38.9875   $38.99   $39.00   $39.00  
  7 purchase totals = $973.38       $1,060.7891   $1,060.79   $1,060.80   $1,060.80