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 $86.60   6.453%   $92.1883   $92.19   $92.20   $92.20  
  Purchase #2 $187.97   12.425%   $211.3253   $211.33   $211.35   $211.30  
  Purchase #3 $121.88   11.153%   $135.4733   $135.47   $135.45   $135.50  
  Purchase #4 $50.69   7.442%   $54.4623   $54.46   $54.45   $54.50  
  Purchase #5 $222.74   5.270%   $234.4784   $234.48   $234.50   $234.50  
  Purchase #6 $214.72   13.415%   $243.5247   $243.52   $243.50   $243.50  
  Purchase #7 $47.57   8.789%   $51.7509   $51.75   $51.75   $51.80  
  7 purchase totals = $932.17       $1,023.2032   $1,023.20   $1,023.20   $1,023.30