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 $61.93   10.614%   $68.5033   $68.50   $68.50   $68.50  
  Purchase #2 $147.41   4.358%   $153.8341   $153.83   $153.85   $153.80  
  Purchase #3 $9.91   7.158%   $10.6194   $10.62   $10.60   $10.60  
  Purchase #4 $17.59   9.560%   $19.2716   $19.27   $19.25   $19.30  
  Purchase #5 $36.54   7.715%   $39.3591   $39.36   $39.35   $39.40  
  Purchase #6 $160.32   13.103%   $181.3267   $181.33   $181.35   $181.30  
  Purchase #7 $219.25   6.580%   $233.6767   $233.68   $233.70   $233.70  
  7 purchase totals = $652.95       $706.5909   $706.59   $706.60   $706.60