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 $151.87   6.114%   $161.1553   $161.16   $161.15   $161.20  
  Purchase #2 $155.80   12.385%   $175.0958   $175.10   $175.10   $175.10  
  Purchase #3 $246.65   9.796%   $270.8118   $270.81   $270.80   $270.80  
  Purchase #4 $80.33   8.597%   $87.236   $87.24   $87.25   $87.20  
  Purchase #5 $152.68   5.801%   $161.537   $161.54   $161.55   $161.50  
  Purchase #6 $214.99   8.512%   $233.2899   $233.29   $233.30   $233.30  
  Purchase #7 $233.40   10.530%   $257.977   $257.98   $258.00   $258.00  
  7 purchase totals = $1,235.72       $1,347.1028   $1,347.12   $1,347.15   $1,347.10