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 $87.34   10.790%   $96.764   $96.76   $96.75   $96.80  
  Purchase #2 $21.69   12.250%   $24.347   $24.35   $24.35   $24.30  
  Purchase #3 $111.39   13.448%   $126.3697   $126.37   $126.35   $126.40  
  Purchase #4 $89.66   6.753%   $95.7147   $95.71   $95.70   $95.70  
  Purchase #5 $247.80   13.313%   $280.7896   $280.79   $280.80   $280.80  
  Purchase #6 $100.62   13.837%   $114.5428   $114.54   $114.55   $114.50  
  Purchase #7 $60.96   12.119%   $68.3477   $68.35   $68.35   $68.30  
  7 purchase totals = $719.46       $806.8755   $806.87   $806.85   $806.80