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 $203.53   5.152%   $214.0159   $214.02   $214.00   $214.00  
  Purchase #2 $111.51   8.425%   $120.9047   $120.90   $120.90   $120.90  
  Purchase #3 $223.85   3.638%   $231.9937   $231.99   $232.00   $232.00  
  Purchase #4 $75.99   6.164%   $80.674   $80.67   $80.65   $80.70  
  Purchase #5 $44.61   7.109%   $47.7813   $47.78   $47.80   $47.80  
  Purchase #6 $209.26   3.465%   $216.5109   $216.51   $216.50   $216.50  
  Purchase #7 $70.73   4.694%   $74.0501   $74.05   $74.05   $74.10  
  7 purchase totals = $939.48       $985.9306   $985.92   $985.90   $986.00