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 $119.95   13.537%   $136.1876   $136.19   $136.20   $136.20  
  Purchase #2 $97.72   13.450%   $110.8633   $110.86   $110.85   $110.90  
  Purchase #3 $215.89   6.535%   $229.9984   $230.00   $230.00   $230.00  
  Purchase #4 $51.81   8.831%   $56.3853   $56.39   $56.40   $56.40  
  Purchase #5 $168.79   4.385%   $176.1914   $176.19   $176.20   $176.20  
  Purchase #6 $153.39   10.803%   $169.9607   $169.96   $169.95   $170.00  
  Purchase #7 $168.62   7.354%   $181.0203   $181.02   $181.00   $181.00  
  7 purchase totals = $976.17       $1,060.6070   $1,060.61   $1,060.60   $1,060.70