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 $91.36   12.773%   $103.0294   $103.03   $103.05   $103.00  
  Purchase #2 $247.65   6.116%   $262.7963   $262.80   $262.80   $262.80  
  Purchase #3 $87.51   8.356%   $94.8223   $94.82   $94.80   $94.80  
  Purchase #4 $193.34   4.477%   $201.9958   $202.00   $202.00   $202.00  
  Purchase #5 $28.55   13.595%   $32.4314   $32.43   $32.45   $32.40  
  Purchase #6 $165.91   9.243%   $181.2451   $181.25   $181.25   $181.20  
  Purchase #7 $139.69   9.738%   $153.293   $153.29   $153.30   $153.30  
  7 purchase totals = $954.01       $1,029.6133   $1,029.62   $1,029.65   $1,029.50