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 $55.40   9.563%   $60.6979   $60.70   $60.70   $60.70  
  Purchase #2 $96.34   8.281%   $104.3179   $104.32   $104.30   $104.30  
  Purchase #3 $204.81   10.311%   $225.928   $225.93   $225.95   $225.90  
  Purchase #4 $48.70   10.399%   $53.7643   $53.76   $53.75   $53.80  
  Purchase #5 $69.86   3.142%   $72.055   $72.06   $72.05   $72.10  
  Purchase #6 $193.72   9.148%   $211.4415   $211.44   $211.45   $211.40  
  Purchase #7 $188.62   4.752%   $197.5832   $197.58   $197.60   $197.60  
  7 purchase totals = $857.45       $925.7878   $925.79   $925.80   $925.80