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 $60.58   13.770%   $68.9219   $68.92   $68.90   $68.90  
  Purchase #2 $241.26   5.250%   $253.9262   $253.93   $253.95   $253.90  
  Purchase #3 $199.41   6.248%   $211.8691   $211.87   $211.85   $211.90  
  Purchase #4 $159.33   12.686%   $179.5426   $179.54   $179.55   $179.50  
  Purchase #5 $51.36   9.514%   $56.2464   $56.25   $56.25   $56.20  
  Purchase #6 $215.60   6.120%   $228.7947   $228.79   $228.80   $228.80  
  Purchase #7 $17.25   8.289%   $18.6799   $18.68   $18.70   $18.70  
  7 purchase totals = $944.79       $1,017.9808   $1,017.98   $1,018.00   $1,017.90