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 $65.46   11.404%   $72.9251   $72.93   $72.95   $72.90  
  Purchase #2 $212.72   6.285%   $226.0895   $226.09   $226.10   $226.10  
  Purchase #3 $144.88   13.127%   $163.8984   $163.90   $163.90   $163.90  
  Purchase #4 $129.98   3.586%   $134.6411   $134.64   $134.65   $134.60  
  Purchase #5 $194.89   3.874%   $202.44   $202.44   $202.45   $202.40  
  Purchase #6 $158.85   11.702%   $177.4386   $177.44   $177.45   $177.40  
  Purchase #7 $14.30   4.453%   $14.9368   $14.94   $14.95   $14.90  
  7 purchase totals = $921.08       $992.3695   $992.38   $992.45   $992.20