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 $32.78   5.754%   $34.6662   $34.67   $34.65   $34.70  
  Purchase #2 $231.80   9.473%   $253.7584   $253.76   $253.75   $253.80  
  Purchase #3 $217.92   13.629%   $247.6203   $247.62   $247.60   $247.60  
  Purchase #4 $154.97   11.526%   $172.8318   $172.83   $172.85   $172.80  
  Purchase #5 $177.74   6.513%   $189.3162   $189.32   $189.30   $189.30  
  Purchase #6 $104.70   8.741%   $113.8518   $113.85   $113.85   $113.90  
  Purchase #7 $179.53   7.253%   $192.5513   $192.55   $192.55   $192.60  
  7 purchase totals = $1,099.44       $1,204.5960   $1,204.60   $1,204.55   $1,204.70