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 $56.59   11.551%   $63.1267   $63.13   $63.15   $63.10  
  Purchase #2 $51.58   9.321%   $56.3878   $56.39   $56.40   $56.40  
  Purchase #3 $55.82   3.339%   $57.6838   $57.68   $57.70   $57.70  
  Purchase #4 $221.98   12.471%   $249.6631   $249.66   $249.65   $249.70  
  Purchase #5 $210.91   12.148%   $236.5313   $236.53   $236.55   $236.50  
  Purchase #6 $93.53   8.555%   $101.5315   $101.53   $101.55   $101.50  
  Purchase #7 $250.25   6.874%   $267.4522   $267.45   $267.45   $267.50  
  7 purchase totals = $940.66       $1,032.3764   $1,032.37   $1,032.45   $1,032.40