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 $247.78   5.851%   $262.2776   $262.28   $262.30   $262.30  
  Purchase #2 $147.81   8.627%   $160.5616   $160.56   $160.55   $160.60  
  Purchase #3 $217.98   7.216%   $233.7094   $233.71   $233.70   $233.70  
  Purchase #4 $5.57   8.584%   $6.0481   $6.05   $6.05   $6.00  
  Purchase #5 $192.98   9.340%   $211.0043   $211.00   $211.00   $211.00  
  Purchase #6 $153.56   3.668%   $159.1926   $159.19   $159.20   $159.20  
  Purchase #7 $16.35   3.689%   $16.9532   $16.95   $16.95   $17.00  
  7 purchase totals = $982.03       $1,049.7468   $1,049.74   $1,049.75   $1,049.80