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 $218.76   8.568%   $237.5034   $237.50   $237.50   $237.50  
  Purchase #2 $197.78   7.802%   $213.2108   $213.21   $213.20   $213.20  
  Purchase #3 $102.71   8.363%   $111.2996   $111.30   $111.30   $111.30  
  Purchase #4 $45.59   7.833%   $49.1611   $49.16   $49.15   $49.20  
  Purchase #5 $76.57   3.560%   $79.2959   $79.30   $79.30   $79.30  
  Purchase #6 $121.53   13.597%   $138.0544   $138.05   $138.05   $138.10  
  Purchase #7 $239.93   10.368%   $264.8059   $264.81   $264.80   $264.80  
  7 purchase totals = $1,002.87       $1,093.3311   $1,093.33   $1,093.30   $1,093.40