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 $181.29   8.656%   $196.9825   $196.98   $197.00   $197.00  
  Purchase #2 $89.80   7.449%   $96.4892   $96.49   $96.50   $96.50  
  Purchase #3 $31.73   12.111%   $35.5728   $35.57   $35.55   $35.60  
  Purchase #4 $245.86   9.420%   $269.02   $269.02   $269.00   $269.00  
  Purchase #5 $217.44   7.534%   $233.8219   $233.82   $233.80   $233.80  
  Purchase #6 $217.76   3.810%   $226.0567   $226.06   $226.05   $226.10  
  Purchase #7 $216.30   8.374%   $234.413   $234.41   $234.40   $234.40  
  7 purchase totals = $1,200.18       $1,292.3561   $1,292.35   $1,292.30   $1,292.40