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 $88.37   11.779%   $98.7791   $98.78   $98.80   $98.80  
  Purchase #2 $239.71   6.113%   $254.3635   $254.36   $254.35   $254.40  
  Purchase #3 $217.98   12.312%   $244.8177   $244.82   $244.80   $244.80  
  Purchase #4 $163.60   12.140%   $183.461   $183.46   $183.45   $183.50  
  Purchase #5 $223.62   3.806%   $232.131   $232.13   $232.15   $232.10  
  Purchase #6 $134.87   9.122%   $147.1728   $147.17   $147.15   $147.20  
  Purchase #7 $82.56   7.523%   $88.771   $88.77   $88.75   $88.80  
  7 purchase totals = $1,150.71       $1,249.4961   $1,249.49   $1,249.45   $1,249.60