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 $116.26   12.712%   $131.039   $131.04   $131.05   $131.00  
  Purchase #2 $118.89   3.739%   $123.3353   $123.34   $123.35   $123.30  
  Purchase #3 $87.78   12.409%   $98.6726   $98.67   $98.65   $98.70  
  Purchase #4 $218.75   5.215%   $230.1578   $230.16   $230.15   $230.20  
  Purchase #5 $121.58   11.397%   $135.4365   $135.44   $135.45   $135.40  
  Purchase #6 $100.99   6.146%   $107.1968   $107.20   $107.20   $107.20  
  Purchase #7 $188.80   3.402%   $195.223   $195.22   $195.20   $195.20  
  7 purchase totals = $953.05       $1,021.0610   $1,021.07   $1,021.05   $1,021.00