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 $232.28   13.122%   $262.7598   $262.76   $262.75   $262.80  
  Purchase #2 $35.39   5.133%   $37.2066   $37.21   $37.20   $37.20  
  Purchase #3 $64.67   4.425%   $67.5316   $67.53   $67.55   $67.50  
  Purchase #4 $237.48   3.288%   $245.2883   $245.29   $245.30   $245.30  
  Purchase #5 $250.48   5.780%   $264.9577   $264.96   $264.95   $265.00  
  Purchase #6 $60.85   12.177%   $68.2597   $68.26   $68.25   $68.30  
  Purchase #7 $212.29   7.126%   $227.4178   $227.42   $227.40   $227.40  
  7 purchase totals = $1,093.44       $1,173.4215   $1,173.43   $1,173.40   $1,173.50