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 $186.34   9.324%   $203.7143   $203.71   $203.70   $203.70  
  Purchase #2 $28.74   3.662%   $29.7925   $29.79   $29.80   $29.80  
  Purchase #3 $79.59   7.460%   $85.5274   $85.53   $85.55   $85.50  
  Purchase #4 $218.33   9.252%   $238.5299   $238.53   $238.55   $238.50  
  Purchase #5 $91.29   13.152%   $103.2965   $103.30   $103.30   $103.30  
  Purchase #6 $56.98   6.248%   $60.5401   $60.54   $60.55   $60.50  
  Purchase #7 $246.26   7.616%   $265.0152   $265.02   $265.00   $265.00  
  7 purchase totals = $907.53       $986.4159   $986.42   $986.45   $986.30