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 $93.68   3.353%   $96.8211   $96.82   $96.80   $96.80  
  Purchase #2 $11.45   3.683%   $11.8717   $11.87   $11.85   $11.90  
  Purchase #3 $202.88   10.112%   $223.3952   $223.40   $223.40   $223.40  
  Purchase #4 $186.29   11.539%   $207.786   $207.79   $207.80   $207.80  
  Purchase #5 $75.96   3.360%   $78.5123   $78.51   $78.50   $78.50  
  Purchase #6 $69.68   10.270%   $76.8361   $76.84   $76.85   $76.80  
  Purchase #7 $235.30   13.826%   $267.8326   $267.83   $267.85   $267.80  
  7 purchase totals = $875.24       $963.0550   $963.06   $963.05   $963.00