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 $205.74   13.276%   $233.054   $233.05   $233.05   $233.10  
  Purchase #2 $247.75   7.381%   $266.0364   $266.04   $266.05   $266.00  
  Purchase #3 $201.73   7.474%   $216.8073   $216.81   $216.80   $216.80  
  Purchase #4 $174.75   11.267%   $194.4391   $194.44   $194.45   $194.40  
  Purchase #5 $241.85   4.332%   $252.3269   $252.33   $252.35   $252.30  
  Purchase #6 $195.94   7.398%   $210.4356   $210.44   $210.45   $210.40  
  Purchase #7 $177.98   4.641%   $186.2401   $186.24   $186.25   $186.20  
  7 purchase totals = $1,445.74       $1,559.3394   $1,559.35   $1,559.40   $1,559.20