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 $143.97   6.276%   $153.0056   $153.01   $153.00   $153.00  
  Purchase #2 $229.36   5.288%   $241.4886   $241.49   $241.50   $241.50  
  Purchase #3 $222.58   10.615%   $246.2069   $246.21   $246.20   $246.20  
  Purchase #4 $206.67   11.127%   $229.6662   $229.67   $229.65   $229.70  
  Purchase #5 $87.51   9.329%   $95.6738   $95.67   $95.65   $95.70  
  Purchase #6 $226.66   6.373%   $241.105   $241.11   $241.10   $241.10  
  Purchase #7 $179.59   5.486%   $189.4423   $189.44   $189.45   $189.40  
  7 purchase totals = $1,296.34       $1,396.5884   $1,396.60   $1,396.55   $1,396.60