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 $235.41   9.841%   $258.5767   $258.58   $258.60   $258.60  
  Purchase #2 $120.87   7.712%   $130.1915   $130.19   $130.20   $130.20  
  Purchase #3 $86.92   11.242%   $96.6915   $96.69   $96.70   $96.70  
  Purchase #4 $35.29   11.631%   $39.3946   $39.39   $39.40   $39.40  
  Purchase #5 $246.98   8.751%   $268.5932   $268.59   $268.60   $268.60  
  Purchase #6 $9.35   5.424%   $9.8571   $9.86   $9.85   $9.90  
  Purchase #7 $148.88   3.862%   $154.6297   $154.63   $154.65   $154.60  
  7 purchase totals = $883.70       $957.9343   $957.93   $958.00   $958.00