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 $118.94   11.742%   $132.9059   $132.91   $132.90   $132.90  
  Purchase #2 $53.45   10.356%   $58.9853   $58.99   $59.00   $59.00  
  Purchase #3 $173.60   11.258%   $193.1439   $193.14   $193.15   $193.10  
  Purchase #4 $83.56   5.433%   $88.0998   $88.10   $88.10   $88.10  
  Purchase #5 $198.50   8.755%   $215.8787   $215.88   $215.90   $215.90  
  Purchase #6 $182.78   6.190%   $194.0941   $194.09   $194.10   $194.10  
  Purchase #7 $153.80   13.605%   $174.7245   $174.72   $174.70   $174.70  
  7 purchase totals = $964.63       $1,057.8322   $1,057.83   $1,057.85   $1,057.80