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 $213.54   13.103%   $241.5201   $241.52   $241.50   $241.50  
  Purchase #2 $179.59   10.450%   $198.3572   $198.36   $198.35   $198.40  
  Purchase #3 $150.89   13.453%   $171.1892   $171.19   $171.20   $171.20  
  Purchase #4 $83.75   4.857%   $87.8177   $87.82   $87.80   $87.80  
  Purchase #5 $117.61   9.525%   $128.8124   $128.81   $128.80   $128.80  
  Purchase #6 $220.80   10.543%   $244.0789   $244.08   $244.10   $244.10  
  Purchase #7 $86.37   6.106%   $91.6438   $91.64   $91.65   $91.60  
  7 purchase totals = $1,052.55       $1,163.4193   $1,163.42   $1,163.40   $1,163.40