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 $177.39   7.679%   $191.0118   $191.01   $191.00   $191.00  
  Purchase #2 $102.74   10.641%   $113.6726   $113.67   $113.65   $113.70  
  Purchase #3 $193.96   9.616%   $212.6112   $212.61   $212.60   $212.60  
  Purchase #4 $200.51   6.117%   $212.7752   $212.78   $212.80   $212.80  
  Purchase #5 $108.87   4.678%   $113.9629   $113.96   $113.95   $114.00  
  Purchase #6 $132.46   6.619%   $141.2275   $141.23   $141.25   $141.20  
  Purchase #7 $33.42   9.406%   $36.5635   $36.56   $36.55   $36.60  
  7 purchase totals = $949.35       $1,021.8247   $1,021.82   $1,021.80   $1,021.90