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 $140.26   8.588%   $152.3055   $152.31   $152.30   $152.30  
  Purchase #2 $164.97   7.404%   $177.1844   $177.18   $177.20   $177.20  
  Purchase #3 $135.44   7.207%   $145.2012   $145.20   $145.20   $145.20  
  Purchase #4 $118.90   8.126%   $128.5618   $128.56   $128.55   $128.60  
  Purchase #5 $109.60   3.753%   $113.7133   $113.71   $113.70   $113.70  
  Purchase #6 $246.30   11.532%   $274.7033   $274.70   $274.70   $274.70  
  Purchase #7 $35.58   13.664%   $40.4417   $40.44   $40.45   $40.40  
  7 purchase totals = $951.05       $1,032.1112   $1,032.10   $1,032.10   $1,032.10