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 $236.67   5.427%   $249.5141   $249.51   $249.50   $249.50  
  Purchase #2 $8.57   12.862%   $9.6723   $9.67   $9.65   $9.70  
  Purchase #3 $67.31   9.766%   $73.8835   $73.88   $73.90   $73.90  
  Purchase #4 $163.56   5.337%   $172.2892   $172.29   $172.30   $172.30  
  Purchase #5 $121.51   3.817%   $126.148   $126.15   $126.15   $126.10  
  Purchase #6 $213.95   11.866%   $239.3373   $239.34   $239.35   $239.30  
  Purchase #7 $169.45   13.140%   $191.7157   $191.72   $191.70   $191.70  
  7 purchase totals = $981.02       $1,062.5601   $1,062.56   $1,062.55   $1,062.50