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 $108.35   10.225%   $119.4288   $119.43   $119.45   $119.40  
  Purchase #2 $92.51   3.434%   $95.6868   $95.69   $95.70   $95.70  
  Purchase #3 $74.44   6.771%   $79.4803   $79.48   $79.50   $79.50  
  Purchase #4 $147.28   11.167%   $163.7268   $163.73   $163.75   $163.70  
  Purchase #5 $240.38   8.435%   $260.6561   $260.66   $260.65   $260.70  
  Purchase #6 $54.95   7.193%   $58.9026   $58.90   $58.90   $58.90  
  Purchase #7 $238.83   6.115%   $253.4345   $253.43   $253.45   $253.40  
  7 purchase totals = $956.74       $1,031.3159   $1,031.32   $1,031.40   $1,031.30