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 $70.59   9.566%   $77.3426   $77.34   $77.35   $77.30  
  Purchase #2 $71.96   6.444%   $76.5971   $76.60   $76.60   $76.60  
  Purchase #3 $224.41   10.425%   $247.8047   $247.80   $247.80   $247.80  
  Purchase #4 $181.60   11.736%   $202.9126   $202.91   $202.90   $202.90  
  Purchase #5 $7.62   13.527%   $8.6508   $8.65   $8.65   $8.70  
  Purchase #6 $65.83   8.756%   $71.5941   $71.59   $71.60   $71.60  
  Purchase #7 $204.94   8.397%   $222.1488   $222.15   $222.15   $222.10  
  7 purchase totals = $826.95       $907.0507   $907.04   $907.05   $907.00