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 $46.31   6.654%   $49.3915   $49.39   $49.40   $49.40  
  Purchase #2 $205.64   11.670%   $229.6382   $229.64   $229.65   $229.60  
  Purchase #3 $180.92   4.822%   $189.644   $189.64   $189.65   $189.60  
  Purchase #4 $234.85   6.840%   $250.9137   $250.91   $250.90   $250.90  
  Purchase #5 $148.39   8.832%   $161.4958   $161.50   $161.50   $161.50  
  Purchase #6 $224.67   9.687%   $246.4338   $246.43   $246.45   $246.40  
  Purchase #7 $123.91   3.699%   $128.4934   $128.49   $128.50   $128.50  
  7 purchase totals = $1,164.69       $1,256.0104   $1,256.00   $1,256.05   $1,255.90