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 $159.65   9.511%   $174.8343   $174.83   $174.85   $174.80  
  Purchase #2 $134.91   5.518%   $142.3543   $142.35   $142.35   $142.40  
  Purchase #3 $207.36   4.224%   $216.1189   $216.12   $216.10   $216.10  
  Purchase #4 $250.79   4.717%   $262.6198   $262.62   $262.60   $262.60  
  Purchase #5 $224.30   5.218%   $236.004   $236.00   $236.00   $236.00  
  Purchase #6 $116.80   3.213%   $120.5528   $120.55   $120.55   $120.60  
  Purchase #7 $83.40   6.841%   $89.1054   $89.11   $89.10   $89.10  
  7 purchase totals = $1,177.21       $1,241.5895   $1,241.58   $1,241.55   $1,241.60