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 $175.92   13.715%   $200.0474   $200.05   $200.05   $200.00  
  Purchase #2 $193.31   10.149%   $212.929   $212.93   $212.95   $212.90  
  Purchase #3 $40.47   10.311%   $44.6429   $44.64   $44.65   $44.60  
  Purchase #4 $246.85   13.600%   $280.4216   $280.42   $280.40   $280.40  
  Purchase #5 $181.40   4.182%   $188.9861   $188.99   $189.00   $189.00  
  Purchase #6 $95.85   11.115%   $106.5037   $106.50   $106.50   $106.50  
  Purchase #7 $68.91   8.479%   $74.7529   $74.75   $74.75   $74.80  
  7 purchase totals = $1,002.71       $1,108.2836   $1,108.28   $1,108.30   $1,108.20