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 $111.88   10.709%   $123.8612   $123.86   $123.85   $123.90  
  Purchase #2 $86.58   8.137%   $93.625   $93.63   $93.65   $93.60  
  Purchase #3 $246.83   10.384%   $272.4608   $272.46   $272.45   $272.50  
  Purchase #4 $211.98   9.655%   $232.4467   $232.45   $232.45   $232.40  
  Purchase #5 $162.40   13.760%   $184.7462   $184.75   $184.75   $184.70  
  Purchase #6 $49.71   3.322%   $51.3614   $51.36   $51.35   $51.40  
  Purchase #7 $64.95   13.487%   $73.7098   $73.71   $73.70   $73.70  
  7 purchase totals = $934.33       $1,032.2111   $1,032.22   $1,032.20   $1,032.20