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 $203.50   11.134%   $226.1577   $226.16   $226.15   $226.20  
  Purchase #2 $23.74   5.205%   $24.9757   $24.98   $25.00   $25.00  
  Purchase #3 $154.41   8.542%   $167.5997   $167.60   $167.60   $167.60  
  Purchase #4 $111.72   11.558%   $124.6326   $124.63   $124.65   $124.60  
  Purchase #5 $249.55   12.364%   $280.4044   $280.40   $280.40   $280.40  
  Purchase #6 $67.49   11.746%   $75.4174   $75.42   $75.40   $75.40  
  Purchase #7 $176.26   11.641%   $196.7784   $196.78   $196.80   $196.80  
  7 purchase totals = $986.67       $1,095.9659   $1,095.97   $1,096.00   $1,096.00