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 $212.37   10.664%   $235.0171   $235.02   $235.00   $235.00  
  Purchase #2 $20.38   6.395%   $21.6833   $21.68   $21.70   $21.70  
  Purchase #3 $69.71   10.244%   $76.8511   $76.85   $76.85   $76.90  
  Purchase #4 $226.56   10.782%   $250.9877   $250.99   $251.00   $251.00  
  Purchase #5 $116.51   10.546%   $128.7971   $128.80   $128.80   $128.80  
  Purchase #6 $8.47   13.356%   $9.6013   $9.60   $9.60   $9.60  
  Purchase #7 $73.69   9.226%   $80.4886   $80.49   $80.50   $80.50  
  7 purchase totals = $727.69       $803.4262   $803.43   $803.45   $803.50