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 $191.77   11.550%   $213.9194   $213.92   $213.90   $213.90  
  Purchase #2 $153.43   7.673%   $165.2027   $165.20   $165.20   $165.20  
  Purchase #3 $134.59   6.522%   $143.368   $143.37   $143.35   $143.40  
  Purchase #4 $134.51   11.749%   $150.3136   $150.31   $150.30   $150.30  
  Purchase #5 $213.28   3.647%   $221.0583   $221.06   $221.05   $221.10  
  Purchase #6 $223.54   4.233%   $233.0024   $233.00   $233.00   $233.00  
  Purchase #7 $7.74   8.698%   $8.4132   $8.41   $8.40   $8.40  
  7 purchase totals = $1,058.86       $1,135.2776   $1,135.27   $1,135.20   $1,135.30