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 $24.28   9.327%   $26.5446   $26.54   $26.55   $26.50  
  Purchase #2 $168.49   7.244%   $180.6954   $180.70   $180.70   $180.70  
  Purchase #3 $200.43   8.784%   $218.0358   $218.04   $218.05   $218.00  
  Purchase #4 $132.50   9.654%   $145.2916   $145.29   $145.30   $145.30  
  Purchase #5 $212.26   7.337%   $227.8335   $227.83   $227.85   $227.80  
  Purchase #6 $210.77   10.635%   $233.1854   $233.19   $233.20   $233.20  
  Purchase #7 $146.37   13.415%   $166.0055   $166.01   $166.00   $166.00  
  7 purchase totals = $1,095.10       $1,197.5918   $1,197.60   $1,197.65   $1,197.50