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 $134.83   12.240%   $151.3332   $151.33   $151.35   $151.30  
  Purchase #2 $187.41   8.132%   $202.6502   $202.65   $202.65   $202.70  
  Purchase #3 $80.70   7.445%   $86.7081   $86.71   $86.70   $86.70  
  Purchase #4 $135.93   13.569%   $154.3743   $154.37   $154.35   $154.40  
  Purchase #5 $91.64   13.122%   $103.665   $103.67   $103.65   $103.70  
  Purchase #6 $163.67   6.428%   $174.1907   $174.19   $174.20   $174.20  
  Purchase #7 $129.75   10.834%   $143.8071   $143.81   $143.80   $143.80  
  7 purchase totals = $923.93       $1,016.7286   $1,016.73   $1,016.70   $1,016.80