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 $197.56   12.170%   $221.6031   $221.60   $221.60   $221.60  
  Purchase #2 $247.39   4.224%   $257.8398   $257.84   $257.85   $257.80  
  Purchase #3 $29.27   5.471%   $30.8714   $30.87   $30.85   $30.90  
  Purchase #4 $111.52   12.130%   $125.0474   $125.05   $125.05   $125.00  
  Purchase #5 $140.77   11.533%   $157.005   $157.01   $157.00   $157.00  
  Purchase #6 $218.57   5.481%   $230.5498   $230.55   $230.55   $230.50  
  Purchase #7 $8.91   3.454%   $9.2178   $9.22   $9.20   $9.20  
  7 purchase totals = $953.99       $1,032.1343   $1,032.14   $1,032.10   $1,032.00