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 $121.93   9.704%   $133.7621   $133.76   $133.75   $133.80  
  Purchase #2 $101.77   4.816%   $106.6712   $106.67   $106.65   $106.70  
  Purchase #3 $77.29   12.824%   $87.2017   $87.20   $87.20   $87.20  
  Purchase #4 $248.30   8.462%   $269.3111   $269.31   $269.30   $269.30  
  Purchase #5 $83.58   13.688%   $95.0204   $95.02   $95.00   $95.00  
  Purchase #6 $208.68   6.753%   $222.7722   $222.77   $222.75   $222.80  
  Purchase #7 $152.58   4.808%   $159.916   $159.92   $159.90   $159.90  
  7 purchase totals = $994.13       $1,074.6547   $1,074.65   $1,074.55   $1,074.70