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 $39.59   10.236%   $43.6424   $43.64   $43.65   $43.60  
  Purchase #2 $228.59   7.407%   $245.5217   $245.52   $245.50   $245.50  
  Purchase #3 $131.68   4.217%   $137.2329   $137.23   $137.25   $137.20  
  Purchase #4 $162.52   9.445%   $177.87   $177.87   $177.85   $177.90  
  Purchase #5 $190.91   5.321%   $201.0683   $201.07   $201.05   $201.10  
  Purchase #6 $57.71   10.167%   $63.5774   $63.58   $63.60   $63.60  
  Purchase #7 $170.88   13.514%   $193.9727   $193.97   $193.95   $194.00  
  7 purchase totals = $981.88       $1,062.8854   $1,062.88   $1,062.85   $1,062.90