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 $88.62   12.499%   $99.6966   $99.70   $99.70   $99.70  
  Purchase #2 $140.68   3.118%   $145.0664   $145.07   $145.05   $145.10  
  Purchase #3 $23.50   12.748%   $26.4958   $26.50   $26.50   $26.50  
  Purchase #4 $165.58   4.245%   $172.6089   $172.61   $172.60   $172.60  
  Purchase #5 $219.83   11.562%   $245.2467   $245.25   $245.25   $245.20  
  Purchase #6 $176.90   4.206%   $184.3404   $184.34   $184.35   $184.30  
  Purchase #7 $242.52   11.709%   $270.9167   $270.92   $270.90   $270.90  
  7 purchase totals = $1,057.63       $1,144.3715   $1,144.39   $1,144.35   $1,144.30