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 $160.45   10.219%   $176.8464   $176.85   $176.85   $176.80  
  Purchase #2 $42.85   4.313%   $44.6981   $44.70   $44.70   $44.70  
  Purchase #3 $33.29   3.793%   $34.5527   $34.55   $34.55   $34.60  
  Purchase #4 $238.86   3.830%   $248.0083   $248.01   $248.00   $248.00  
  Purchase #5 $183.90   12.840%   $207.5128   $207.51   $207.50   $207.50  
  Purchase #6 $85.85   10.286%   $94.6805   $94.68   $94.70   $94.70  
  Purchase #7 $240.91   5.456%   $254.054   $254.05   $254.05   $254.10  
  7 purchase totals = $986.11       $1,060.3528   $1,060.35   $1,060.35   $1,060.40