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 $77.29   6.721%   $82.4847   $82.48   $82.50   $82.50  
  Purchase #2 $139.66   11.873%   $156.2418   $156.24   $156.25   $156.20  
  Purchase #3 $230.95   5.740%   $244.2065   $244.21   $244.20   $244.20  
  Purchase #4 $198.87   6.340%   $211.4784   $211.48   $211.50   $211.50  
  Purchase #5 $201.30   6.107%   $213.5934   $213.59   $213.60   $213.60  
  Purchase #6 $81.85   12.832%   $92.353   $92.35   $92.35   $92.40  
  Purchase #7 $66.37   13.496%   $75.3273   $75.33   $75.35   $75.30  
  7 purchase totals = $996.29       $1,075.6851   $1,075.68   $1,075.75   $1,075.70