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 $238.95   5.575%   $252.2715   $252.27   $252.25   $252.30  
  Purchase #2 $165.94   8.498%   $180.0416   $180.04   $180.05   $180.00  
  Purchase #3 $87.70   6.426%   $93.3356   $93.34   $93.35   $93.30  
  Purchase #4 $224.99   3.560%   $232.9996   $233.00   $233.00   $233.00  
  Purchase #5 $85.85   3.282%   $88.6676   $88.67   $88.65   $88.70  
  Purchase #6 $225.98   10.226%   $249.0887   $249.09   $249.10   $249.10  
  Purchase #7 $197.26   3.225%   $203.6216   $203.62   $203.60   $203.60  
  7 purchase totals = $1,226.67       $1,300.0262   $1,300.03   $1,300.00   $1,300.00