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 $111.90   5.652%   $118.2246   $118.22   $118.20   $118.20  
  Purchase #2 $161.89   6.714%   $172.7593   $172.76   $172.75   $172.80  
  Purchase #3 $194.62   12.817%   $219.5644   $219.56   $219.55   $219.60  
  Purchase #4 $33.68   3.307%   $34.7938   $34.79   $34.80   $34.80  
  Purchase #5 $230.92   6.593%   $246.1446   $246.14   $246.15   $246.10  
  Purchase #6 $133.57   5.814%   $141.3358   $141.34   $141.35   $141.30  
  Purchase #7 $66.72   13.552%   $75.7619   $75.76   $75.75   $75.80  
  7 purchase totals = $933.30       $1,008.5844   $1,008.57   $1,008.55   $1,008.60