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 $32.50   4.491%   $33.9596   $33.96   $33.95   $34.00  
  Purchase #2 $228.75   11.791%   $255.7219   $255.72   $255.70   $255.70  
  Purchase #3 $241.66   13.257%   $273.6969   $273.70   $273.70   $273.70  
  Purchase #4 $198.93   7.459%   $213.7682   $213.77   $213.75   $213.80  
  Purchase #5 $190.78   4.229%   $198.8481   $198.85   $198.85   $198.80  
  Purchase #6 $235.68   7.693%   $253.8109   $253.81   $253.80   $253.80  
  Purchase #7 $106.58   13.417%   $120.8798   $120.88   $120.90   $120.90  
  7 purchase totals = $1,234.88       $1,350.6854   $1,350.69   $1,350.65   $1,350.70