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 $203.97   9.215%   $222.7658   $222.77   $222.75   $222.80  
  Purchase #2 $177.73   4.119%   $185.0507   $185.05   $185.05   $185.10  
  Purchase #3 $123.60   13.115%   $139.8101   $139.81   $139.80   $139.80  
  Purchase #4 $140.30   8.119%   $151.691   $151.69   $151.70   $151.70  
  Purchase #5 $243.84   7.386%   $261.85   $261.85   $261.85   $261.90  
  Purchase #6 $187.95   7.170%   $201.426   $201.43   $201.45   $201.40  
  Purchase #7 $249.51   13.421%   $282.9967   $283.00   $283.00   $283.00  
  7 purchase totals = $1,326.90       $1,445.5903   $1,445.60   $1,445.60   $1,445.70