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 $177.61   9.491%   $194.467   $194.47   $194.45   $194.50  
  Purchase #2 $39.29   5.343%   $41.3893   $41.39   $41.40   $41.40  
  Purchase #3 $208.34   11.708%   $232.7324   $232.73   $232.75   $232.70  
  Purchase #4 $244.65   3.247%   $252.5938   $252.59   $252.60   $252.60  
  Purchase #5 $235.89   12.243%   $264.77   $264.77   $264.75   $264.80  
  Purchase #6 $50.31   4.158%   $52.4019   $52.40   $52.40   $52.40  
  Purchase #7 $30.73   5.179%   $32.3215   $32.32   $32.30   $32.30  
  7 purchase totals = $986.82       $1,070.6759   $1,070.67   $1,070.65   $1,070.70