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 $88.55   5.806%   $93.6912   $93.69   $93.70   $93.70  
  Purchase #2 $7.98   5.205%   $8.3954   $8.40   $8.40   $8.40  
  Purchase #3 $117.92   6.496%   $125.5801   $125.58   $125.60   $125.60  
  Purchase #4 $82.64   10.580%   $91.3833   $91.38   $91.40   $91.40  
  Purchase #5 $221.61   4.226%   $230.9752   $230.98   $231.00   $231.00  
  Purchase #6 $161.91   9.599%   $177.4517   $177.45   $177.45   $177.50  
  Purchase #7 $64.86   10.265%   $71.5179   $71.52   $71.50   $71.50  
  7 purchase totals = $745.47       $798.9948   $799.00   $799.05   $799.10